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

compiler/guards.nim

@@ -249,6 +249,9 @@ proc pred(n: PNode): PNode =
   else:
     result = n
 
+proc buildLe*(o: Operators; a, b: PNode): PNode =
+  result = o.opLe.buildCall(a, b)
+
 proc canon*(n: PNode; o: Operators): PNode =
   if n.safeLen >= 1:
     result = shallowCopy(n)