Unify exception hierarchy in type module and other minor fixes.

### AST test:
* Improve test coverage of module to 100%.

### Errata:
* Add entry about valid argument types in constructors.
* Sort all entries.

### Symbol:
* Rename `SymbolTable` to `Table`.

### Type:
* Unify error hierarchy.

### Type test:
* Adapt tests to new error hierarchy.