Bug fixes and extensions of existing methods

[stevengoossensB]

• Fixed a bug in the 'T' function to have the same behaviour as Excel
• Fixed compatibility with reference to a Cell if the name is referenced as RC
• Added support for arithmetic operators on dates

[DissectMalware]

The code does not work correctly after this commit https://github.com/DissectMalware/XLMMacroDeobfuscator/pull/65/commits/b7a22c863c6b37db2c82809f60777e63bda87632

Example: 6f6ba7e59949cd4869f4cd3d63d556b86313b7e42d2030546426efbef20ee2c1

The output after this commit is

Instead of https://pastebin.com/cZ5kKQLn

The code is already merged with master.