Initial rough commit adding doubles to expression parser/evaluator.
Switch to doubles for internal function calculation.
Bugfixes: expression parsing and evaluation now supports doubles.
Enabled support for double-precision floating point signals.
Merge branch 'master' into doubles
Fix reference to MAPPER_NOW.
Merge branch 'doubles' into merge-doubles

Conflicts:
	src/expression.c
	test/testparser.c
Add remaining cast operations, cast output as necessary.
Use run-time type casting where appropriate.
Copy expression output when type is double.