* Modernize to ES6 and give a feature boost
Motive:
* support multiple fits of extentionless targets.
* let user decide on order of tried extensions for extensionless targets
* support custom merge
Also accomplished:
* support a list of targets
* file-mapper gets also path
* support separate onItrErr handler, defaults to onLoadErr
* let user inject custom loaders by file-pattern. user may shadow existing loaders if his loaders match first
* add tests - WIP
* .travis - update target versions
* try coveralls integration
* 100% coverage
* mainly readme updates, not finished
* improve tests output
* include in package only production files
* improve tests
* fix broken test
* update README.md
* fix stupid bug :o\
* Update README.md
* improve consistency - treat directory as a type of file
* Update README.md
* Update README.md
* Update README.md
* Update README.md
* cleanup tests + allow run specific cases
* Update README.md
Co-authored-by: Админ <larisayablonskaya@gmail.com>