Added bitslice operations for bitops (#14016)

* 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()

changelog.md

@@ -61,6 +61,10 @@
 - `paramCount` & `paramStr` are now defined in os.nim instead of nimscript.nim for nimscript/nimble.
 - `dollars.$` now works for unsigned ints with `nim js`
 
+- Improvements to the `bitops` module, including bitslices, non-mutating versions
+  of the original masking functions, `mask`/`masked`, and varargs support for
+  `bitand`, `bitor`, and `bitxor`.
+
 - `sugar.=>` and `sugar.->` changes: Previously `(x, y: int)` was transformed
   into `(x: auto, y: int)`, it now becomes `(x: int, y: int)` in consistency
   with regular proc definitions (although you cannot use semicolons).