Bug/issue#97 (#102)

This addresses all of the compiler warnings and errors for xlc when compiled at -O0. There are still compiler bugs when compiling with higher optimization levels, however they are more challenging.

* Ignore the incorrect `-Wno-missing-braces` warnings (similarly to Clang).
* Remove `-qhalt=e flag` inserted by CMake.
* Remove redundant comparison of char to EOF in lexer.
* The XLC compiler was crashing inexplicably on one call of the following method:
   ```void run(..., const std::vector<float>& excl={}) {...}```
  This was fixed by not having a default value for the last argument.
* Add some curly braces to silence warning for dangling else.

fixes #97