add `Plugins::Redcarpet#rouge_formatter`

Override this method to provide custom formatting behavior in the redcarpet plugin.
Derp. put the method in the right place.
v1.3.0
add a desc for gherkin and the behat alias
fill in a couple of lexer descriptions
v1.3.1
grammar is hard
add ruby 2.1 to CI
install fewer gems on ci
force a bundler update on ci
remove rubinius from the ci build :(

no workeee
c family: allow 100e-2 as a Num::Float
cpp: allow single quotes as digit separators

as in

    int foo = 100'000'000
dev bugfix: require the development gems

in the visual spec app
bugfix: highlight %= properly in ruby
move Lexer.load_const to Lexers
v1.3.2
add newlines to the end of html output
add the :push special name
python: quit pasting regexes together with |

attempt at #127