Update comments on general architecture.

Narrow IL code backwords, so as to correctly handle invocations to overloaded functions from IL code.

Code cleanup.

Add printing of semantic errors when calling FB from IL.

Fix typo error in some il visit in fill_candidate_datatypes_c class.

Add semantic verification of FB calls in IL (not yet complete - missing printing of errors!)

Add support for semantic verification of function calls in IL.

Add TODO comment, and delete unused debugging code.

Delete un-used code.

Change negation expression (neg_expression_c) to only allow signed data types.

Move elementary_c::to_string() to datatype_functions.cc/hh

Add, to types symbol table, string datatypes with limited length (my_string_type: STRING[33]) (Thanks Andreas!)

Correctly return the initial value of a string datatype, with limited length (STRING[33] := 'hello')

More detailed error messages for FB invocations in ST.

More detailed error messages in function invocations in ST.

Fix bug in analysing real literals (thanks Andreas!)

Remove debugging messages, and code cleanup.

Better error reporting in function invocations, and in invalid literal values.

Better identification of erros in function/FB invocations.

Print error messages when datatype erros found in ST function/FB calls.

Continue checking data type compatibility inside expressions used to pass paramters to invalid function/FB calls

Adding support for semantic verification of FB calls in ST.

Delete wrong comment.

Add support in stage 3 for checking function invocations in ST.

Fix search_varfb_instance_decl to be able to find variables and FB when only given an identifier.
Fix handling of FB calls in stage3.
Start handling of function invocations in stage3.

Changing code indenting.

Add fill candidate method for fb_invocation_c symbol.

Re-write of stage3 code (done by Manuele and I), re-write of search_varfb_instance_type_c (done by myself), and several other bug fixes.

Merging with Laurent's repository.

Fix YYLTYPE declaration.