Use the power of regexp to replace #strip

Parsing rake task arguments used strip to remove whitespace from tokens
but we can use the regular expression to avoid capturing the whitespace
in the first place.
Use regexp capture groups over matchdata

Now we can assign directly to local variables since rake only supports
ruby 1.9 and newer.  This also reduces our line count.
Use gsub properly

Since the token is not reused elsewhere a plain gsub is preferred over
gsub! with an ||.
Use named captures for parsing task arguments

This follows @5db0bae and reduces use of globals.  The next refactor
will flip the logic around to make it cleaner.
Fail early from parse_task_string

This makes the method a little easier to follow.
Reduce work in parsing task arguments

Flipping the conditional makes this easier to understand, too.
Fit to 80 columns and remove superfluous comments
Fail early in task argument parsing (again)

This reduces indentation for the begin end while loop.
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