Add a retab utility

Usage: tools/dev/retab.rb directory

will retab with 2-width spaces rather than tabs for indentation.

This utility should be used by the @tabassassin account when it's
unleashed on the Metasploit code base in order to make git blame a
little easier to spot. (diffs should use -b or -w to avoid seeing
@tabassassin's changes)
Add *.notab to gitignore

These are artifacts of tools/dev/retab.rb
Adds a test module for space checking

This module should throw three errors on lines 17, 18, and 19 when
checked against the new msftidy.rb that is space-tolerant (but not
tab-space tolerant)
Allow for tabs or spaces as indentation

This signals a move to allowing for normal Ruby indentation (2 space
soft tabs). This change will check files for indentation of spaces or of
tabs, since we don't want to fail out all modules quite yet.

For more, see
https://github.com/rapid7/metasploit-framework/wiki/Indentation-Standards
where all details of the conversion plan will be documented in order to
minimize the amount of whitespace conflict we are sure to encounter over
this conversion.
Add some old hard-tabs for sanity
Land #2197 - Tabassassin msftidy