Picture Catalog

Rust study: local picture file catalog with emphasis on identifying duplicates and adding missing Exif fields e.g. dates.

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When in airplane mode, Rust setup out of the box is surprisingly functional, here are a few easy hints:

Start a local server for Rust documentation, available on http://[::1]:8001 or http://localhost:8001; can also use rustup doc without a Web server:
```
python3 -m http.server --bind localhost --directory "$(dirname $(rustup doc --path))" 8001 &
```
Generate documentation for the project and its dependencies and place in target/doc/; use a similar Python HTTP server as above to view it nicely formatted and browsable on http://[::1]:8002/ or http://localhost:8002. I didn't find --open option all that useful due to poor browser rendering of files served from local file system:
```
cargo doc --document-private-items

python3 -m http.server --bind localhost --directory ./target/doc 8002 &
```
One more notable feature in the previous item is that formatted source code of dependency crates can be found in target/doc/src and comes handy for studying other people's coding.