Updated README.md and RST Documentation

[robfrawley]

Major refactoring of documentation (both in README.md and RST documentation).

Markdown README

To view how the updated README.md renders, reference robfrawley/LiipImagineBundle/blob/feature-update-docs/README.md.

ReStructuredText DOCS

To view how the updated docs render, reference src.run/docs/symfony_build/liipimaginebundle where I've compiled a build reflective of this pull-request.

The docs were built using a clone of the official Symfony Docs Repo with the required fabpot/sphinx-php python package, as well as the nessissary system binaries. Due to less-than-perfect build-conditions, as well as a lack of documentation as to how Symfony actually performs their documentation compilation, you'll notice that many of the ancillary links in the above referenced build are dead. Don't fret; our only concern is ensuring the links within the liipimaginebundle folder of the build function properly: the links to Symfony and other components are immaterial in this context.

To better understand the doc build handling for the official documentation, reference the _build directory of the official Symfony Docs Repo.

[alexwilson]

This is honestly really great and should help newcomers a lot! 👍

[lsmith77]

@javiereguiluz can you have a look?

[javiereguiluz]

In Symfony Docs we usually put the label before the section title. Otherwise, when clicking a link with this anchor, you don't have a clear reference about where you are.

[javiereguiluz]

@robfrawley you did a huge and great work in this PR. I left some minor comments, mostly related to missing double backticks for <code> element. But overall looks OK to me 👍 Thanks!

[robfrawley]

Thanks for taking the time to review the PR @javiereguiluz! Very much appreciated. I implemented all your changes, minus the backtick comments, as can be seen in this diff.

As for the backticks, I started using .. default-role:: code about halfway through, as it makes it much easier to copy and paste between markdown and RST when both use single backticks. Problem is, it wasn't standardized because I'd started halfway through writing the docs. As such, I updates all the RST files to use the .. default-role:: code statement at the start and standardized on single backticks. Is this acceptable?

[robfrawley]

@lsmith77 After @javiereguiluz okays my last comment, please give me a shout if you want me to squash commits before PR merge. I left the latest commits intact so @javiereguiluz could see a diff of the changes from his comments easily.

[javiereguiluz]

About the default-role ... I'm not sure if ti's going to work. We can merge this and then revert if it's not working ass expected. In any case, all Symfony Docs use the double backticks ... and it shouldn't be hard to do it with a Find + Replace + Regex in your editor 😄

[robfrawley]

@javiereguiluz No worries; I've just updated the PR to use double back ticks everywhere to avoid the uncertainty.

[robfrawley]

@lsmith77 With this reviewed by @javiereguiluz, I think it is now ready to be merged! Please advise if you want the PR squashed before merge.