We add clippy as our build — also rectifying the missing `plume-cli` build!
In the next step we follow clippy's advise and fix some of the "simple" mistakes in our code, such as style or map usage.
Finally, we refactor some hard bits that need extraction of new types, or refactoring of function call-types, especially those that thread thru macros, and, of course functions with ~15 parameters should probably be rethought.
All the template are now compiled at compile-time with the `ructe` crate.
I preferred to use it instead of askama because it allows more complex Rust expressions, where askama only supports a small subset of expressions and doesn't allow them everywhere (for instance, `{{ macro!() | filter }}` would result in a parsing error).
The diff is quite huge, but there is normally no changes in functionality.
Fixes#161 and unblocks #110 and #273
