EncodedData was setting "converter" and "_encoding" by setting them on the
prototype of the object. This was probably done to enable overriding these
functions. However, overriding was never actually used anywhere, and setting
the __proto__ is deprecated. So I have remove all instances of setting
__proto__ for EncodedData-ish classes, and instead just set "convert" and
"_encoding" on the object directly.
...no longer relies on Manuel's repo hostig a version of "bignum" that actually
contained bignumber.js. This moves bignumber.js internally and removes bignum
from the browser build process. Also adds a bitcore.Bignum that links to the
right thing. In node, browser.Bignum is require('bignum'). And in the browser,
bitcore.Bignum is is now Bignumber.js (same as before ... except bignumber.js
is now inside bitcore).