ENH: Add additional 32-bit floating point output

Add 32-bit float support for exponentials
Refactor distribution.c to avoid code duplication
Refactor ziggurat constants to separate header
Use better names for _double and _float core RNG

Author: bashtage

README.md

@@ -23,13 +23,33 @@ same seed, same random numbers).
 * Support for random number generators that support independent streams 
 and jumping ahead so that substreams can be generated
 * Faster random number generation, especially for Normals using the 
-Ziggurat method 
+Ziggurat method
 
 ```python
 import randomstate as rnd
 w = rnd.standard_normal(10000, method='zig')
 ```
 
+* Preliminary support for 32-bit floating randoms for core generators. 
+  Currently only uniforms (`random_sample`) and exponentials 
+  (`standard_exponential`) have been implemented. Ultimately support 
+  should be avialable for:
+  
+    * Uniforms
+    * Exponentials
+    * Standard Gammas (via `standard_gamma`)
+    * Normals (via `standard_normal`)
+  
+  **WARNING**: The 32-bit generators are **experimental** and subjust 
+  to change.
+  
+  **Note**: There are no plans to extend the alternative precision generation to 
+  all random number types.
+  
+  
+  
+
+
 ## Included Pseudo Random Number Generators
 
 This modules includes a number of alternative random 

README.rst

@@ -31,6 +31,22 @@ Features
     import randomstate as rnd
     w = rnd.standard_normal(10000, method='zig')
 
+-  Preliminary support for 32-bit floating randoms for core generators.
+   Currently only uniforms (``random_sample``) and exponentials
+   (``standard_exponential``) have been implemented. Ultimately support
+   should be avialable for:
+
+   -  Uniforms
+   -  Exponentials
+   -  Standard Gammas (via ``standard_gamma``)
+   -  Normals (via ``standard_normal``)
+
+**WARNING**: The 32-bit generators are **experimental** and subjust to
+change.
+
+**Note**: There are no plans to extend the alternative precision
+generation to all random number types.
+
 Included Pseudo Random Number Generators
 ----------------------------------------
 
@@ -61,6 +77,9 @@ New Features
    argument which can be ``bm`` or ``zig`` where ``bm`` corresponds to
    the current method using the Box-Muller transformation and ``zig``
    uses the much faster (100%+) ziggurat method.
+-  ``random_sample`` can produce either single precision
+   (``np.float32``) or double precision (``np.float64``, the default)
+   using an the optional keyword argument ``dtype``.
 
 New Functions
 ~~~~~~~~~~~~~