Delete Gemfile.lock.

Per Yehuda Katz's advice[0], ditch the specific versions of gems specified
in the Gemfile.lock so that we are forced to get the dependencies
specified correctly in our Gemfile (or future gemspec).

[0]: http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/
Gemify!

Write a simple gemspec, move things into their appropriate directories,
and add a little Rake task to make it easier to generate a gem, install
it, publish it, etc.

Fixes #43.
Update installation instructions.

Also, fix incorrect ordering of example `ln` command.
Re-add readline import.

I mistakenly removed it in 84c9127 because I thought it had been
replaced entirely by highline in addd628; this is not true.

Readline is part of the standard library, so there's no need to include
it in the dependency list.
Merge gemify (#48) into master

Gemify!

Write a simple gemspec, move things into their appropriate directories,
and add a little Rake task to make it easier to generate a gem, install
it, publish it, etc.

Fixes #43.