`v1.4.0` Release

[Radonirinaunimi]

This issue collects what should go into the next v1.4.0, to decouple them from more fundamental changes such as #370 and #392 (?) which will eventually go into v1.5.0. These include fixes and documentations that have already been merged:

• bumping of MSRV to v1.94.0 Bum MSRV to 1.94.0 #382
• bug fixes and various improvements Improve ConvFuns detection #390, Fix fastNLO import with two scales #387, Various API fixes #380
• various updates on the documentations Improve and update deprecated documentations #378

As well as still open issues on improving the documentations.

[cschwan]

We should use Github's milestone features to mark thing we want to include.

[cschwan]

One potential pitfall of the MSRV change is that RTD doesn't seem to support it yet. One potential solution could be to sneak in a --ignore-rust-version (some cargo applets support it), because the code actually doesn't use any features of Rust 1.92, 1.93 or 1.94 (yet).

[felixhekhorn]

since any change of supported version on RTD might be slow (is there any record on the speed?), it might be better to lower MSRV down to 1.91 instead