* Allow let to not have value when using importc
This allows a let statement with the `{.importc.}` pragma to not be
initialised with a value. This allows us to declare C constants as Nim
lets without putting the value in the Nim code (which can lead to
errors, and requires us to go looking for the value). Fixes#14253
* Proper fix and documentation + changelog entry
* Improve testcase with one from timotheecour
* Add test to verify it working with macros
* do not track 'raise Defect' in the .raises: [] clause anymore
* --panics:on maps 'raise Defect' to an unrecoverable fatal error
* make tests green again
* update the documentation too
* `nim doc --backend:js|cpp...`
`nim doc --doccmd:'-d:foo --threads:on'`
`nim r --backend:cpp...` (implies --run --usenimcache)
* --usenimcache works with all targets
* --docCmd:skip now skips compiling snippets; 50X speedup for doc/manual.rst
* * fix regression: -d:nimHasLibFFI was not being tested anymore,
in part because testament was silently treating some errors as easy to overlook messages
* turned that message into an error
* -d:nimHasLibFFI is now being tested with nim cpp
* use correct signatures for importc procs
* workaround for openbsd to unblock ctffi testing
* added bit operations based on bit slices, clarified documentation, made non-mutating versions of mask ops
* Added since annotations, some runnable examples
* Added mask()/masked() functions, changed internal workings of mask ops to use new bit* funcs
* Changelog updated for new bitops improvements
* Reorganization, added runnable examples
* Documentation adjustments
* Add incltrl for since annotation
* Fix masked() impl
* Fix mask() return type
* Don't call toUnsigned on already unsigned types
* Remove improper `var T` for flipMasked()
* Fix return types for flipMasked()
* Slight syntactic cleanup for *masked ops
* Added tests for bitslice operations, new mask() operation, non-mutating mask ops
* Fix setmasked() var T issue
* More comprehensive tests
* Fix runnable example for bitsliced()
* Fix runnable example for mask()
* fix https://github.com/timotheecour/Nim/issues/152 `^[[0m` is inserted in stderr for `echo code | nim c -`
* resetAttributes not even needed, already handled in styledWriteLine
* simplify tests in tests/trunner.nim thanks to this fix
* added high level sendTo and recvFrom to std/asyncnet; tests were also added.
* add .since annotation, a changelog entry and fixed to standard library style guide.
* Improved asserts msgs and added notes for use with UDP sockets
* pointers removed in parameters and fixes
* added .since annotation
* minor fixes
