implemented bno_usub, untested.  bnu_tstr next.
Added tostring for bignums
BN_ZERO is now a quick initializer instead of bni_zero() and fixed compiler errors in bn add
Added safety checks for trim and resize
Beginning of multiplication.  LShift/RShift must be added first.  After robocop.
Created left bitshift.  Untested as of yet.
Some documentation and added lshift to header.  Time to test
Fixed.  Shift distance was off, correct now.  Begin rshift.
ignore debug symbols
rshift would appear to work :D