compiler/libec: (#205) Corrections to integer promotions

compiler/libec: (#205) Corrections to integer promotions
- Not promoting assignment operations
- Skipping warnings on | and & operator
- Not adding casts to integer constants fitting within a char or a short
- Tweaks to not warn on uncasted conditional expressions as the compiler will already have warned on if/else operands
- Modified MatchTypeExpression to use constant expressions within brackets