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

drnim/tests/tensures.nim

@@ -0,0 +1,31 @@
+discard """
+  nimout: '''tensures.nim(11, 10) Warning: BEGIN [User]
+tensures.nim(20, 5) Warning: cannot prove:
+0 < n [IndexCheck]
+tensures.nim(30, 10) Warning: END [User]'''
+  cmd: "drnim $file"
+  action: "compile"
+"""
+
+{.push staticBoundChecks: defined(nimDrNim).}
+{.warning: "BEGIN".}
+
+proc fac(n: int) {.requires: n > 0.} =
+  discard
+
+proc g(): int {.ensures: result > 0.} =
+  result = 10
+
+fac 7 # fine
+fac -45 # wrong
+
+fac g() # fine
+
+proc main =
+  var x = g()
+  fac x
+
+main()
+
+{.warning: "END".}
+{.pop.}