Strip dependencies of bat-as-a-library

[dtolnay]

Fixes #895. This PR introduces a features = ["application"] which is enabled by default and pulls in everything required by bat the application. When depending on bat as a library, downstream Cargo.toml should disable this feature to cut out inapplicable heavy dependencies like liquid.

[dependencies]
bat = { version = "0.13", default-features = false }

I've put some other optional functionality behind features as well: paging and git support, neither of which I would want for cargo-expand.

[sharkdp]

Thank you very much! This looks great 👍

[sharkdp]

Thank you for the updates.

Note that we still pull in clap as a dependency via syntect=>onig=>onig_sys=>bindgen (https://github.com/rust-lang/rust-bindgen/blob/f568d095774bd5642fe8404e13268e43bd47327a/Cargo.toml#L50-L51). But this could be resolved by upgrading to syntect 4.1.0 and making it possible to use fancy-regex as you suggested in #896.

[sharkdp]

But this could be resolved by upgrading to syntect 4.1.0 and making it possible to use fancy-regex as you suggested in #896.

See #900