Remove unused dashmap dependency

[xmakro]

Also increments version. Please push a new release.

Pinning the version of dashmap means that crates that depend on html2text cannot use a newer version of dashmap

[jugglerchris]

It's definitely a mistake that dashmap is a non-optional dependency - it should only be used when the css feature is enabled.

However, it's there for a reason - I'm currently aiming to support Rust 1.63 (in current stable Debian), and dashmap 5.5+ has a higher MSRV. (dashmap is a dependency of lightningcss, the CSS parser currently used) I had to add that for the CI test with 1.63 to pass.

Do you need the CSS feature? If not then making it optional and enabled with the css feature would be fine.

In the slightly longer term I'm replacing lightningcss (which is also relatively huge) with a much smaller CSS parser which won't have the dashmap dependency at all.

[xmakro]

Thanks, I changed it to optional, that works for my case. Hopefully in the future this version pinning can be avoided:
rust-lang/rfcs#3537
rust-lang/cargo#9930