The new `to` operators that can be used to constuct Stint types from
regular integer types. These are intented for usage in generic code
such as rlp.nim
Also fixes a bug preventing construction of Stint values from unsigned
integers (because they lack an unary `-` operator).
* Refactor asSignedWords, kill 130+ lines
* Allow signed int initialization at compiletime.
* inline procs in uint_mul
* Fix an unfortunate shadowing in high(Int)
* Initial commit - allow all ops at compile-time on uint.
* Update benchmark
* Delete commented ideal version of asWordsiterate, it is obvious from the workaround (and is tracked in the PR)
* Start on allowing compile-time stint. Works for Uint256
* remove and reorder initUintImpl, zero and one procs
* Fix assignation of uint64 to 2xuint32, remove unsafeConv and use const for base/radix
* assign_least_significant_words shouldn't implicitly capture result
* Simplify least significant words macros
