fix #62 (toast now addressed relatively); macros=>procs + other fixes (#70)

* fixes https://github.com/genotrance/nimterop/issues/62
*  toast is now automatically built on demand, and doesn't depend on PATH
- [ ] todo: need to track its deps properly to trigger rebuilding it; using same algo as shown here https://github.com/genotrance/nimterop/issues/69 but using nim deps instead of c deps
* many other fixes
  * trying to follow https://github.com/timotheecour/vitanim/wiki/Nim-best-practices

config.nims

@@ -1,3 +1,8 @@
+#[
+see D20190127T231316 workaround for fact that toast needs to build scanner.cc, which would otherwise result in link erros such as:
+"std::terminate()", referenced from:
+      ___clang_call_terminate in scanner.cc.o
+]#
 when defined(MacOSX):
   switch("clang.linkerexe", "g++")
 else: