DOC: splitting the IO docs into separate pages
The documentation on the extensive pandas IO tools is currently one big page: http://pandas.pydata.org/pandas-docs/stable/io.html. 

I propose to split this in several files: a page with a general introduction to the IO tools, and then one page per format (writer/reader combo). 
(this could be seen as a first start for #6000)

Splitting this shouldn't be that hard (I was just a bit experimenting if it would be possible to keep git blame working for all splitted files, but not that important probably ..), but an issue I would like to get some feedback for: **What do we do with all existing links? How do we keep them working?**

Anybody who has some experience with such issues when restructuring a website what the best way is to deal with this?
