Support %cat checking $LOAD_PATH directories.
Also files relative to load path dirs.

Oops, fix typo in comments.

Switch to  backticks instead of plusses.

Set and unset  in a context.

Remove unnecessary #basename.

Remove early File#basename so relative paths actually work.
Add cat support for Ruby files with .rb ext omitted.

Add support for %cat with .rb ext omitted.

Allow highlighting ommitted '.rb' ext, DRY up ext checking.

Only call Pry::Code#from_file once on instantiation.
Removed unncessary 'if' check that @kyrylo pointed out.
Fix bug when 'name/' and 'name.rb' both exist.
Merge branch 'cat' of github.com:havenwood/pry into havenwood-cat
lib/pry/code.rb: refactor $LOAD_PATH path finding
spec/code_spec.rb: refactor tests

- Use fixtures as a test files
- Write more concise spec titles
spec/code_spec.rb: add more tests for $LOAD_PATH behaviour
lib/pry/code.rb: remove #known_extensions cruft
lib/pry/code.rb: factor out code related to filename handling

Factor out it to `lib/pry/code/code_file.rb`.
lib/pry/code.rb,lib/pry/code/code_file.rb: add docs
lib/pry/code/code_file.rb: fix typo in #code