Converted documentation into reStructuredText format

[javiereguiluz]

This fixes #236.

[stof]

compiling and testing might be placed in a separate section than installation and usage, as they are about contributing to the bundle, not about using it (or their content might be moved to a CONTRIBUTING.md file rather than the doc)

[javiereguiluz]

I've done every suggested change. Ready for the second review round!

[javiereguiluz]

In case this PR dropped off the radar of the maintainers, I'm pinging about it. This bundle is so popular that it would be nice to have its documentation on symfony.com. Thanks!

[willdurand]

Thanks @javiereguiluz

[javiereguiluz]

Thanks for merging ... this should be on symfony.com as soon as these changes are merged on master branch too. Thanks!

[stof]

@javiereguiluz done.

Please make /current point to the 1.x doc of the bundle for now though if possible.

[javiereguiluz]

@stof thanks for merging this. The new docs will be published on symfony.com after the next deploy. Sadly I can't configure the /current shortcut as requested. I've created an issue about that to see if we can fix it. Thanks!