Can be used like this:
```
$ cargo run --release -p ra_cli -- \
analysis-bench ../chalk/ \
--complete ../chalk/chalk-engine/src/logic.rs:94:0
loading: 225.970093ms
from scratch: 8.492373325s
no change: 445.265µs
trivial change: 95.631242ms
```
Or like this:
```
$ cargo run --release -p ra_cli -- \
analysis-bench ../chalk/ \
--highlight ../chalk/chalk-engine/src/logic.rs
loading: 209.873484ms
from scratch: 9.504916942s
no change: 7.731119ms
trivial change: 124.984039ms
```
"from scratch" includes initial analysis of the relevant bits of the
project
"no change" just asks the same question for the second time. It
measures overhead on assembling the answer outside of salsa.
"trivial change" doesn't do an actual salsa change, it just advances
the revision. This test how fast is salsa at validating things.
`ProjectWorkspace::to_roots` now returns a new `ProjectRoot` which contains
information regarding whether or not the given path is part of the current
workspace or an external dependency. This information can then be used in
`ra_batch` and `ra_lsp_server` to implement more advanced filtering. This allows
us to filter some unnecessary folders from external dependencies such as tests,
examples and benches.
Instead of using canonicalize, we now join the given path to
`std::env::current_dir()`, which either replaces the path, if the given path is
absolute, or joins the paths.
This fixes#821.
