New techs: js-link and json-links
js-links - freeze static imgs in js
json-links - freeze dynamic imgs in js
relative paths in require
unit tests
remove process.env.BORSCHIK_FREEZABLE_EXTS
fix @arikon comments
fix tests for json-links
Merge pull request #80 from doochik/freeze-imgs-in-js

New techs: js-link and json-links