removed trailing whitespace instances
added support for Host aliases (and alias,unalias commands)

the ssh_config man page mentions that Host lines may contain "more
than one pattern... separated by whitespace".  I personally make use
of this feature, and discovered that this tool didn't handle that case
very well.  So, I added support for it, including:

- when parsing the file, treat multiple whitespace-separate items as a
  name and a list of aliases.

- Allow matching for 'show' command against an alias (also allowed
  multiple name/alias arguments).

- added an 'alias' command to create new aliases.

- added an 'unalias' command to remove aliases.

- updated documentation accordingly.

- minor cleanup (removal of trailing whitespace, error reporting, etc.)
Merge pull request #2 from lindes/master

Added support for Host-line aliases, plus minor cleanup