DrNim (Nim compiler with Z3 integration) (#13743)

* code cleanups and feature additions
* added basic test and koch/CI integration
* make it build on Unix
* DrNim: now buildable on Unix, only takes 10 minutes, enjoy
* added basic documentation for DrNim which can also be seen as the RFC we're following
* drnim: change the build setup so that drnim.exe ends up in bin/
* makes simple floating point ranges work
* added basic float range check
* drnim: teach Z3 about Nim's range types plus code refactoring
* drnim: make unsigned numbers work
* added and fixed index checking under setLen
* first implementation of .ensures, .invariant and .assume (.requires still missing and so is proc type compatibility checking
* drnim: .requires checking implemented
* drnim: implemented .ensures properly
* more impressive test involving min()
* drnim: check for proc type compatibility and base method compatibility wrt .requires and .ensures
* testament: support for 'pattern <directory>
* koch: uses new <directory> feature of testament
* drnim: added tiny musings about 'old'
* Make testament work with old SSL versions
* koch: add support for 'koch drnim -d:release'
* drnim: preparations for the param.old notation

lib/system/strmantle.nim

@@ -115,6 +115,9 @@ const
               1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19,
               1e20, 1e21, 1e22]
 
+when defined(nimHasInvariant):
+  {.push staticBoundChecks: off.}
+
 proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
                           start = 0): int {.compilerproc.} =
   # This routine attempt to parse float that can parsed quickly.
@@ -236,7 +239,7 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
     # if exponent is greater try to fit extra exponent above 22 by multiplying
     # integer part is there is space left.
     let slop = 15 - kdigits - fdigits
-    if  absExponent <= 22 + slop and not expNegative:
+    if absExponent <= 22 + slop and not expNegative:
       number = sign * integer.float * powtens[slop] * powtens[absExponent-slop]
       return i - start
 
@@ -274,6 +277,9 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
   else:
     number = c_strtod(t, nil)
 
+when defined(nimHasInvariant):
+  {.pop.} # staticBoundChecks
+
 proc nimInt64ToStr(x: int64): string {.compilerRtl.} =
   result = newStringOfCap(sizeof(x)*4)
   result.addInt x