Add positive? and negative? methods

Allows you to compare values against 0 without worrying about
currencies.
Update authors and changelog
Merge pull request #157 from ohthatjames/positive_and_negative

Add positive? and negative? methods
Update README.md
Fix a typo and remove some spaces
Fix format output with thousands separator
Spec for custom currency format output
Update CHANGELOG and AUTHORS files
Merge pull request #156 from alup/master

Fix format output with custom currencies (4 decimal places)
reference GH-165 in @alup's change description
Refactor parsing mechanism to better identify major,minor
Specs for parsing custom currency, strings with 3 decimal digits
Update CHANGELOG
Update travis config
Merge pull request #159 from alup/master

Fix parsing of strings with 3 decimal digits
Fix a typo in README
minor bugfix - incorrect use of character range resulted in botched results for Money::Parsing#extract_cents
fixed some tortured code
added a regression test
Update CHANGELOG.md