Replace rust-i18n with phf string maps and simple replaces

[nc7s]

Alternative to #1426 for comparison. Strings are now &'static str as phf::Map entries, placeholder substitution is simply str::replace, no complex logic. Executable size is down 1MB (!).

Downsides are 1. build.rs, 2. str::replace is not enough for complex translations.

Currently both the $kt:ident = $kt:expr and $kt:literal => $kv:expr forms of t! are still supported, but I doubt if they really differ.

[nc7s]

Failure of the build-docker job seems to be a result of the way Dockerfile is written. The "caching" somehow resulted in build.rs being skipped.

[fujiapple852]

@nc7s I pushed a commit which fixes the Dockerfile. I've not had time to review the rest of this yet, I will over the weekend.

[fujiapple852]

aside: I think this may be broken on master as well, as the locales directory is not copied into the docker image.

edit: yes, broken:

$ docker run -it fujiapple/trippy 1.1.1.1 --print-locales
TUI locales:

bug: #1431