`{.push overflowChecks: off.}` works in backends. Though it could be
implemented as a magic function.
By inspecting the generated C code, the overflow check is eliminated in
the debug or release mode.

Likewise, the index checking is probably not needed.
* system refactor, move out 600 lines
* compilation, slice, backwardsindex, misc_num moved out of system
* some procs/types moved into arithmetics, basic_types
* system no longer depends on syncio
* some procs moved around to fit with their surroundings
* make exceptions an import, old ops to misc_num
* move instantiationInfo back
* move back nim version, fix windows echo
* include compilation
* better docs for imported modules, fix unsigned ops
also remove ze, ze64, toU8, toU16, toU32 with nimPreviewSlimSystem
* fix terminal
* workaround IC test & weird csize bug, changelog
* move NimMajor etc back to compilation, rebase for CI
* try ic fix
* form single `indices`, slim out TaintedString, try fix IC
* fix CI, update changelog, addQuitProc
* fix CI
* try fix CI
* actually fix CI finally hopefully
* Update lib/system/compilation.nim
Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>
* update kochdocs
* hopefully fix csize uses for slimsystem
* fix tquit
Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>
* add enumutils.items for enum with holes
* changelog
* ref in lib.rst
* use `type SomeSparseEnum* = (not Ordinal) and enum` instead of concept
* address comment: rename back to enum with holes
* refactoring: idents don't need inheritance
* refactoring: adding an IdGenerator (part 1)
* refactoring: adding an IdGenerator (part 2)
* refactoring: adding an IdGenerator (part 3)
* refactoring: adding an IdGenerator (part 4)
* refactoring: adding an IdGenerator (part 5)
* refactoring: adding an IdGenerator (part 5)
* IdGenerator must be a ref type; hello world works again
* make bootstrapping work again
* progress: add back the 'exactReplica' ideas
* added back the missing exactReplica hacks
* make tcompilerapi work again
* make important packages green
* attempt to fix the build for 32 bit machines (probably need a better solution here)
* fix pairs, mpairs, mitems for cstring for JS backend
* add mutation check for pairs and mpairs for strings and seqs
* change the assertion message - modifying (changing elements) is not
a problem, changing the length is