removed useless extern func declaration in __INIT_EXTERNAL, producing warning during build of POUS.c

Fixing bug in generated code for complex type external variable

Fixing SUB standard function defined in standard library

Fixing generated code for global variables. Adding support for defining global variables with complex type
Fixing bug preventing to generate SFC transition with IL body

Fixing bug in all SUB function definitions in standard_functions.txt

Fix bug when using enumerated type in equ_expression or notequ_expression

silenced warning on X86_64 build by casying numerical operand of snprintf

Fix bug in generate_c_inlinefcall. Was not handling textual SFC elements

Fix code generation of FOR loops. Now handles negative values of BY correctly.

Fix semantic verification of enumerated data types.

Adding a line to a comment. Does not change any code.

fixed signedness warning on string slicing funcs in std lib

Fix bug generate_c_inlinefcall in inline function name generated

Fix bug in parser while trying to use IL operator like S1, R1, etc... as standard function block interface variable in structured_variable syntax and bug in code generator while generating code for assignment of function block interface variable using structured_variable syntax