Fixes (UglifyJs) lint warnings
   Fix: Symbol exports is declared but not referenced [lib/b64.js:3,12]
   Fix: Symbol ZERO is declared but not referenced [lib/b64.js:10,5]
   Fix: Symbol res is declared but not referenced [test/convert.js:14,1]
Merge pull request #8 from schnittstabil/master

This pull request fixes some lint warnings.