slight changes (~typos) in mathematical optim
minor correction to clarify 'enumerate' is a built-in function

http://docs.python.org/3/library/functions.html#enumerate is a built-in, not a keyword
Update index.rst

I corrected a couple of sentences, and 
I thint that line 131 has an incomplete sentence.
Merge pull request #110 from nicoguaro/patch-1

Update index.rst
updated DiveIntoPython hyperlink

corrected the hyperlink from http://www.diveintopython.org (site not available) to http://www.diveintopython.net/
Merge pull request #111 from hoteit/patch-1

updated DiveIntoPython hyperlink
Merge pull request #107 from mhemantha/patch-1

minor correction to clarify 'enumerate' is a built-in function
Merge pull request #106 from pierre-haessig/optim-enh

slight changes (~typos) in mathematical optim
fix typos
mention reference count bugs
mention section on ref counting and cpychecker
links to the Numpy C-API
tweaks
fix typo
typo discovered during the lecture