Make ninja build rules customizable (not hardcoded to CMake defaults)

Change-Id: I59ab4ed3e8765a177f96c9af8e5b4aaca9c8b73c
Fix incorrect parsing of compiler exe

Change-Id: I0be9e000de353ebc46208cbd277f21914ce18489
Changes to compiler include path processing

- Don't add compiler include paths when parsing command line
- New optional parameter to ede-system-include-path to include/exclude
  compiler paths
- Allow compiler to be a relative path (eg for wrapper scripts)

Change-Id: I79840a0f3afecfd92e7b50416766afaa4aea556a
Document integration with flycheck and company-c-headers

Change-Id: I64ee4f1c0685aefd083ff2d4aec32d650cb0684f