Fix many py2-style prints in docs and commented code.

The main interest was to transform py2-style print statements that still
appeared in some docstrings (e.g. for %history) and would thus show up
when looking at the docs either interactively or in the rendered
website.  I also fixed a number of commented-out print statements at the
same time, mostly because it was easier for me to just regexp-change all
of them so that I could focus on the others.

Author: anntzer

IPython/lib/lexers.py

@@ -456,13 +456,13 @@ def get_mci(self, line):
             # does not use the continuation marker cannot be detected.
             # For example, the 3 in the following is clearly output:
             #
-            #    In [1]: print 3
+            #    In [1]: print(3)
             #    3
             #
             # But the following second line is part of the input:
             #
             #    In [2]: while True:
-            #        print True
+            #        print(True)
             #
             # In both cases, the 2nd line will be 'output'.
             #