Merge branch 'release/0.7'
modifying how option sets are coalesced during parsing to ensure the order the commands are defined, both w/in a command in w/in the command hierarchy is respected.  This way commands on super classes are shown after the commands on the sub classes which ensures the most relevant to the command options are shown first in the usage.
* adding a usage printer for an HTML format, only works for a specific command, does not handle group usage printing
* quick help hack to use the HTML format usage printing if a flag is enabled
* bumping airline rev
Added default command to synopsis.
Titles with multiple names for arguments.

This change adds the posibility to add multiple names for arguments,
e.g.  in a `git remote add` command the arguments can be `name` and
`url`, therefore in the help message it's going to render `<name>` and
`<url>` as separate arguments. A further improvement would be to handle
tpyes and arity for arguments too.
Made a couple of improvements in the help system and the rendering logic.

The changes include:
- showing which is the default command in a command group;
- one can specify multiple separated names for command arguments;
- replaced 'Whith no arguments' by 'By default' in command group message.

Merge branch 'feature/helpText' into develop