Add support for the Colemak-DH keyboard layout
This provides the Colemak-DH layouts for US (ANSI), UK (ISO), and Polish (ISO) keyboards, as defined by the Colemak Mod-DH project.
Justification
You may be wondering what this layout is and why it should be included, so I offer here some background information and evidence that this layout is being actively used.
The Colemak-DH layout originated from the Mod-DH project, and is a modification to the popular Colemak keyboard layout. It was designed to address a couple of common issues that users experienced with standard Colemak. Specifically, Colemak-DH (i) reduces the priority of the centre column keys, and (ii) uses a non-traditional finger assignment scheme for the keys in the bottom-left of the keyboard.
Since it was launched in 2014, Colemak-DH has become a popular mod within the Colemak user community. It is particularly common among users of non-traditional keyboard hardware, such the increasingly popular matrix-like boards, but usage and support is good for traditional hardware too.
The number of users is of course unknown as there is no way to track, but I offer this relevant information:
The Colemak Mod-DH project site visitor stats according to Google Analytics: Last 90 days: 6.2K sessions with 3.5K unique users.
The Colemak-DH github repository has (at time of writing) 116 stars, 33 forked copies, and 8 contributors.
There is an active community of users on the Colemak Forum and on the Colemak Discord server. There are also plenty of relevant threads on Reddit, e.g. in r/Colemak, r/ErgoMechKeyboards/, and r/KeyboardLayouts.
There are also sculpted keycaps available for Colemak-DH.
Colemak-DH is supported by DreymaR's big bag of Keyboard tricks, which is a popular community resource for Colemak and keyboard efficiency hacks.
Colemak-DH is supported by some popular typing tutor sites, e.g.
I hope the above demonstrates that this is a moderately popular layout (by alternative layouts standards!), and is therefore worthy of inclusion.