Fix issue #218
Error message instead of triggering assertion on certain syntax errors

When functions were used without arguments or arrays without indexes an assertion was triggered. Now an error message is printed.
Remove debugging statement.
Fix segfaults in PE module
Add new instructions for working with doubles.
Merge branch 'master' into resource_name_and_entropy

Conflicts:
	libyara/grammar.c
	libyara/modules/pe.c