Link to creating methods in struct documentation

The Rust standard library has a nice practice for documentation for public
structs. Documentation for these structs include links to the method that
creates them. This is very useful for beginners who may stumble upon the
documentation for the struct when they would really like documentation for the
method.

Add documentation for all of the structs that are created by methods on the
`UnicodeSegmentation` trait with links back to the creating methods.

Author: HarrisonMc555

src/grapheme.rs

@@ -13,6 +13,12 @@ use core::cmp;
 use tables::grapheme::GraphemeCat;
 
 /// External iterator for grapheme clusters and byte offsets.
+///
+/// This struct is created by the [`grapheme_indices`] method on the [`UnicodeSegmentation`]
+/// trait. See its documentation for more.
+///
+/// [`grapheme_indices`]: trait.UnicodeSegmentation.html#tymethod.grapheme_indices
+/// [`UnicodeSegmentation`]: trait.UnicodeSegmentation.html
 #[derive(Clone)]
 pub struct GraphemeIndices<'a> {
     start_offset: usize,
@@ -61,6 +67,12 @@ impl<'a> DoubleEndedIterator for GraphemeIndices<'a> {
 
 /// External iterator for a string's
 /// [grapheme clusters](http://www.unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries).
+///
+/// This struct is created by the [`graphemes`] method on the [`UnicodeSegmentation`] trait. See its
+/// documentation for more.
+///
+/// [`graphemes`]: trait.UnicodeSegmentation.html#tymethod.graphemes
+/// [`UnicodeSegmentation`]: trait.UnicodeSegmentation.html
 #[derive(Clone)]
 pub struct Graphemes<'a> {
     string: &'a str,

src/sentence.rs

@@ -274,20 +274,38 @@ mod fwd {
 /// [Alphabetic](http://unicode.org/reports/tr44/#Alphabetic)
 /// property, or with
 /// [General_Category=Number](http://unicode.org/reports/tr44/#General_Category_Values).
+///
+/// This struct is created by the [`unicode_sentences`] method on the [`UnicodeSegmentation`]
+/// trait. See its documentation for more.
+///
+/// [`unicode_sentences`]: trait.UnicodeSegmentation.html#tymethod.unicode_sentences
+/// [`UnicodeSegmentation`]: trait.UnicodeSegmentation.html
 #[derive(Clone)]
 pub struct UnicodeSentences<'a> {
     inner: Filter<USentenceBounds<'a>, fn(&&str) -> bool>,
 }
 
 /// External iterator for a string's
 /// [sentence boundaries](http://www.unicode.org/reports/tr29/#Sentence_Boundaries).
+///
+/// This struct is created by the [`split_sentence_bounds`] method on the [`UnicodeSegmentation`]
+/// trait. See its documentation for more.
+///
+/// [`split_sentence_bounds`]: trait.UnicodeSegmentation.html#tymethod.split_sentence_bounds
+/// [`UnicodeSegmentation`]: trait.UnicodeSegmentation.html
 #[derive(Clone)]
 pub struct USentenceBounds<'a> {
     iter: fwd::SentenceBreaks<'a>,
     sentence_start: Option<usize>
 }
 
 /// External iterator for sentence boundaries and byte offsets.
+///
+/// This struct is created by the [`split_sentence_bound_indices`] method on the
+/// [`UnicodeSegmentation`] trait. See its documentation for more.
+///
+/// [`split_sentence_bound_indices`]: trait.UnicodeSegmentation.html#tymethod.split_sentence_bound_indices
+/// [`UnicodeSegmentation`]: trait.UnicodeSegmentation.html
 #[derive(Clone)]
 pub struct USentenceBoundIndices<'a> {
     start_offset: usize,

src/word.rs

@@ -19,6 +19,12 @@ use tables::word::WordCat;
 /// [Alphabetic](http://unicode.org/reports/tr44/#Alphabetic)
 /// property, or with
 /// [General_Category=Number](http://unicode.org/reports/tr44/#General_Category_Values).
+///
+/// This struct is created by the [`unicode_words`] method on the [`UnicodeSegmentation`] trait. See
+/// its documentation for more.
+///
+/// [`unicode_words`]: trait.UnicodeSegmentation.html#tymethod.unicode_words
+/// [`UnicodeSegmentation`]: trait.UnicodeSegmentation.html
 pub struct UnicodeWords<'a> {
     inner: Filter<UWordBounds<'a>, fn(&&str) -> bool>,
 }
@@ -36,6 +42,12 @@ impl<'a> DoubleEndedIterator for UnicodeWords<'a> {
 
 /// External iterator for a string's
 /// [word boundaries](http://www.unicode.org/reports/tr29/#Word_Boundaries).
+///
+/// This struct is created by the [`split_word_bounds`] method on the [`UnicodeSegmentation`]
+/// trait. See its documentation for more.
+///
+/// [`split_word_bounds`]: trait.UnicodeSegmentation.html#tymethod.split_word_bounds
+/// [`UnicodeSegmentation`]: trait.UnicodeSegmentation.html
 #[derive(Clone)]
 pub struct UWordBounds<'a> {
     string: &'a str,
@@ -44,6 +56,12 @@ pub struct UWordBounds<'a> {
 }
 
 /// External iterator for word boundaries and byte offsets.
+///
+/// This struct is created by the [`split_word_bound_indices`] method on the
+/// [`UnicodeSegmentation`] trait. See its documentation for more.
+///
+/// [`split_word_bound_indices`]: trait.UnicodeSegmentation.html#tymethod.split_word_bound_indices
+/// [`UnicodeSegmentation`]: trait.UnicodeSegmentation.html
 #[derive(Clone)]
 pub struct UWordBoundIndices<'a> {
     start_offset: usize,