Work on string formatting

[CohenArthur]

• Expand simple expressions (variables, constants, arithmetic expressions) Basic string interpolation #183
• Add formatting trait instead of relying on Instruction::(pretty_)print #424
• Allow the use of the delimiter characters by doubling them ("Hello {{}}" becomes "Hello {}") #426
• Forbid usage of certain constructs (LoopBlock, IfElse, VarAssign...) #425
• Allow usage of primitive types in string interpolation #432
• Allow usage of string interpolation in REPL #433
• Parse delimiter escaping correctly #434

Work should be merged on feature/string-interpolation for the time being