Notable changes in Tolk v0.7

1. Under the hood: refactor and revamp compiler internals. AST-level semantic analysis kernel
2. Under the hood: rewrite the type system from Hindley-Milner to static typing
3. Clear and readable error messages on type mismatch
4. Generic functions fun f<T>(...) and instantiations like f<int>(...)
5. The bool type
6. Type casting via value as T

The documentation and IDE plugins have been updated accordingly (see related pull requests below).