* implement arithmetic right shift
* workaround Nim VM 'cast' limitation
* fix high(stint) bug
* fix compile time bit shift bug
* add test for compile time shift and high(stint)
* add tests against ttmath
* remove experimental for loop macro usage
* make implementation of several operations follow data structure
(recursive data -> recursive implementation)
* rename getSize -> bitsof to avoid bits vs bytes confusion
* fix potential 32-bit issue where asSignedWords cast to `int` even when
`uint64` was used as storage
* `hi` for signed ints now is signed - this replaces `asSignedWords` and
makes several int operations more natural
* fix bit size assert
* Refactor asSignedWords, kill 130+ lines
* Allow signed int initialization at compiletime.
* inline procs in uint_mul
* Fix an unfortunate shadowing in high(Int)
