fixes help menu when unknown options are passed
Merge pull request #11 from farfanoide/arguments

adds arguments parsing
Adds -o option to open session files

moves code from inside the main loop to local functions to keep things
more organized.
renames usage function to _usage to be consistent with other local
funcitons and updates it's output.

open/create option:
Discussion should arise here on wether one option should only edit or
both edit/create session files. one could also have a -n(new) option.

note on example files: having an examples folder available would greatly
help when creating new sessions, -n option could receive an
example_session_name which would copy said template in order to rapidly
get new projects up and running.
updates help menu
Merge branch 'open_session' of github.com:farfanoide/tmuxstart into open_session

Conflicts:
	tmuxstart