* `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
* Implement compileSetting() and compileSettingSeq()
* Change from magic to vmop
* better design for querySetting
Co-authored-by: genotrance <dev@genotrance.com>