v2 - Change to yaml.ansible and *.jinja2 (pearofducks#55)

- The filetype for playbooks is now set to `yaml.ansible`.
  - Using a compound filetype here improves compatibility with some other plugins, and is a bit more honest about the filetypes being used. We _could_ set it to `yaml.jinja2.ansible`, if there are strong opinions on this please open an issue.
  - This _only_ breaks setups using vim plugin on-demand loading features — e.g. `{ 'for': 'ansible' }` in vim-plug. Otherwise this change should not break anything.
- `g:ansible_extra_syntaxes` is now deprecated in favor of `g:ansible_template_syntaxes` — which will use conditional compound filetypes, instead of sourcing all filetypes listed and hiding them under `ansible_template`.
  - While this is a complete deprecation of one setting, the new functionality is significantly better all around and should support the same use-cases.
  - Example: a ruby+ansible-template will have a filetype of `ruby.jinja2` instead of `ansible_template`
  
One non-breaking change is also added, this plugin gains additional compatibility with _stephpy/vim-yaml_ — syntax highlights will be improved when using this plugin.

Use sub-bullets instead for change notice

Merge pull request pearofducks#2 from DavidWittman/patch-1

Add documentation of filetypes to README

Cleanup old comments

Fixes pearofducks#1, Ignore is not the same as NONE and I'm a horribl…

…e person for thinking so