added support for external formatter module

formatter name can be any resolvable (npm) module name or path as used by require()
fixed formatterLoader.ts and ruleLoader.ts CORE folders
* made relative to module.filename (instead of implied working directory)
* resolves rules and formatters correctly when tslint is used by dependents (grunt-tshint etc)
* requires to compile tests to ./build (instead of ./build/test, as module.path is the compiled JS file)
added .gitattributes for fixture line-endings