Fixes#1170.
This PR adds the module name to `RefIdent` in order to distinguish
conflicting names from different files. This also fixes related issues
in find-references or the call hierarchy feature.
It also adds some docstrings and stylistically refactors a bunch of
code.
We are considering removing `.` as an alternative for `·` in the
lambda dot notation (e.g., `(·+·)`).
Reasons:
- `.` is not a perfect replacement for `·` (e.g., `(·.insert ·)`)
- `.` is too overloaded: `(f.x)` and `(f .x)` and `(f . x)`. We want to keep the first two.
