Add Syntax::ExampleGroup
Add RSpecVersion#non_monkey_patch_example_group_available?
Introduce -v/--convert option and deprecate -t/--convert-stub-with-hash

Relted to #54.
Colorize help descriptions by markup
Extend line length of help description to 100
Tweak rubocop:disable comment placement
Add alises of example group and example DSL
Add RSpecConfigure#expose_dsl_globally=
Change base node of RSpecConfigure from block to send
Support conversion to non-monkey-patch #describe

This closes #22.
Merge branch 'non-monkey-patch-describe'
Tweak description of -v/--convert
Move position of -s/--skip-dynamic-analysis in option list
Improve description of enabling/disabling conversions