add a few basic ops to BN

eq, gt, geq, lt, leq are extremely useful.
neq

i.e., not equal to
change cmp to eq, neq, gt, geq, lt, leq

These functions are far more readable and make parsing and auditing the code a
lot easier.
rename Signature -> Sig

It is somewhat irritating to type out long names like "Signature". "Sig" is
much friendlier. Also, it is more compatible with the fact that "sig" is the
most often used abbreviation for a signature object throughout the code.
improve wording of comment in index.js
BufferReader/BufferWriter -> BufR/BufW

It is somewhat irritating to type out "BufferReader" or "BufferWriter". The
shorter versions "BufR" and "BufW" are much easier to type out. I also thought
about calling them "BR" and "BW", however that would make them very similar to
"BN", which of course is a completely different class. These new names are very
succinct while also reminding the user about what they are and do.
use BufR convention
v0.3.0