Updates to the documentation

[kaustubhmote]

This PR updates the documentation at these places:

1. New functions in fileio.simpson.py and fileio.bruker.py catalogued
2. A new file for documenting misc.xcpy.py
3. Updated installation instructions and requirements (install.rst)
4. Updated tutorial.rst (correct links, more information on filetypes that nmrglue can handle)
5. Updated instructions to use matplotllib in tutorial.rst

[kaustubhmote]

There are several other places where the documentation needs to be updated, and I'll get to those eventually. But this is what I already had ready, and since the plan is to cut version 0.8 soon, these could possibly go in.

[jjhelmus]

Thanks for putting this together. Looks good overall. I added two comments on minor changes.

[jjhelmus]

LGTM, thanks for the update.