Add expression => self mutation

Also reorganizes parts of meta to align filenames to node name better.

Closes #191
Use non redundant simplecov matcher
Adjust flay score
Avoid mutating break to next

Closes #201
Correct eurucamp conference name
Merge pull request #202 from lucaspinto/master

Correct eurucamp conference name
Do not emit rescue matchers with higher selectabillity

Closes #183
Prepare version 0.5.19
Fix adjacent namespece selections

Closes #167
Do not mutate to invalid AST on reqarg promotion

Closes #153
Allow rspec-3.0.0
Only require minimum parts rspec

This fixes the case people had to explicitly define the 'rspec'
metagem in Gemfile
Adjust flay score
Fix examples in README
Merge pull request #204 from gcapizzi/update_readme_examples

Fix examples in README
Normalize ASTs prior to mutation

This avoids situartions where the source contains (begin, other)
nodes that get mutated to (other) where there is no difference in the
source.

Closes #198
Update badges and donation section
Correct rubygems badge
Correct flattr badge
Sync devtools and fix rubocop warnings