bendc: added code generation for input func args

- The C backend now generates code for function arguments. Nothing too fancy, but a step closer to a useful language.
- Also added a tests directory that contains some random snippets of code.
- Blocks are now available as primary expressions, which allows the programmer to describe an expression's result in terms of a sequence of operations. This gives rise to a language conflict with set literals, as an empty set and an empty block both translate into "{}". Non-empty variants are not an issue, as they translate to "{1,2}" and "{1;2;}".
bendc: implemented function calls

The C backend now generates code for calling other functions.