Reflexivity fo #.atob() & #.btoa()

[jung-kim]

Perhaps it would be better to throw exception or have an option to have such option when length % 4 !==0 or string has white spaces.

> ByteBuffer.btoa(ByteBuffer.atob("a"))
''
> ByteBuffer.btoa(ByteBuffer.atob("ab"))
'aQ=='
> ByteBuffer.btoa(ByteBuffer.atob("abc"))
'abc='
> ByteBuffer.btoa(ByteBuffer.atob("abcd"))
'abcd'
> ByteBuffer.btoa(ByteBuffer.atob("abcde"))
'abcd'
> ByteBuffer.btoa(ByteBuffer.atob("abcdef"))
'abcdeQ=='
> ByteBuffer.btoa(ByteBuffer.atob("abcdefg"))
'abcdefg='
> ByteBuffer.btoa(ByteBuffer.atob("abcdefgh"))
'abcdefgh'
> ByteBuffer.btoa(ByteBuffer.atob("a   "))
''
> ByteBuffer.btoa(ByteBuffer.atob("a111"))
'a111'
> ByteBuffer.btoa(ByteBuffer.atob("a  c"))
'aQ=='
> ByteBuffer.btoa(ByteBuffer.atob("ab c"))
'abc='
> ByteBuffer.btoa(ByteBuffer.atob("abc"))
'abc='

[dcodeIO]

Somehow connected to #60

Currently trying to resolve any encoding issues by adding ByteBuffer-aware implementations, see: https://github.com/dcodeIO/bytebuffer.js/tree/master/src/encodings/impl