Switch template engine to Askama

[noirotm]

This commit has the benefit of improving type safety, as well as reducing code size.

It has been a bit challenging to use Askama, as the documentation isn't that great compared to handlebars, especially regarding custom filters.
For example, surprisingly, {{ a|b }} works, while {{ a | b }} refuses to compile.
It is also a little bit more rigid as templates need to be placed in a dedicated templates directory.

In the end it works fine 😄

[VictorKoenders]

reducing code size.
🎉

as the documentation isn't that great compared to handlebars
This is something I also ran into when I began, but I personally don't see how to fix this

[VictorKoenders]

I wish publish this to crates.io soon-ish, probably within 24 hours

[VictorKoenders]

Released 0.2.0 🎉

Also apparently cargo doesn't like it when you modify the lib.rs during a deploy:

error: failed to verify package tarball

Caused by:
  Source directory was modified by build.rs during cargo publish. Build scripts should not modify anything outside of OUT_DIR.
Added: /home/trangar/development/rust/periodic_table/target/package/periodic_table-0.2.0/src/lib.rs

To proceed despite this, pass the `--no-verify` flag.

[noirotm]

cargo doesn't like it when you modify the lib.rs during a deploy

This could be fixed by following https://doc.rust-lang.org/cargo/reference/build-scripts.html#case-study-code-generation.

Basically, we keep a simple lib.rs which reexports a module written in OUT_DIR. Seems the cleanest thing to do.
I believe Askama itself writes the compiled template in that directory.

Gonna try this today.

[VictorKoenders]

Yes, I think so too. I have opened an issue for this: #7