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).
* Add serialization for decimal and hex
* Fix carry bug in signed add
* Add parsing test
* Improve highlow for int, remove most_significant_word_mut
* make conversion toString compile
* Add division corner case test
* Remove a buggy division shortcut
* Fix decimal string conversion
* Fix hex dumping
* Fix power of 2 division (what was I thinking?)
* Add hexdump test
* Move runtime check to compile-time
* Fix static assert check
* more compile-time asserts
* Fix parsing of negative hex numbers, add test_io to the suite
* dump default to bigEndian, split toString in Stint and Stuint
* Add (failing) tests with big ints conversion
* Temporarily remove all the noInit pragma
