remove deprecated Slop.optspec
remove Slop::Commands as it was originally
move error classes into slop/errors
Slop is now strict by default, and adds --help by default

Also use 1.9 hash syntax
Rename DEFAULT_OPTIONS to DEFAULT_CONFIG to save confusion
drop 1.8 testing support
Slop::Error now has a slop attribute and a help method
Slop is no longer enumerable, you should use Slop#options
Use self prefix for class methods over class << self
Use alias_method over alias
Clean up conditional operators