Improve readability of CHANGELOGs

[ivanperez-keera]

The changelogs currently list the path associated to a change, prior to the summary of the change. For example, Yampa's CHANGELOG recently lists:

Yampa/yampa/CHANGELOG

Lines 1 to 6 in 8461217

	2023-04-07 Ivan Perez <ivan.perez@keera.co.uk>
	* Yampa.cabal: Version bump (0.14.2) (#259).
	* src/: Conformance with style guide (#255).
	* examples/: Conformance with style guide (#255), move example to
	yampa-test library (#257).
	* README: Add game to list of games and apps in README (#254).

The addition of paths to those changes adds very little useful information (if any at all). The decision of how big a part of the path to show in the CHANGELOG (e.g., src/FRP/Yampa.hs vs src/) is quite arbitrary. Adding the paths also implies that, sometimes, a change may have to be listed multiple times, since it affected multiple paths, and the re-wrapping of change summaries to fit in one line makes for awkward diffs and makes reading the changelogs harder.

For an example of a CHANGELOG with no paths, see:

https://github.com/ivanperez-keera/dunai/blob/1755154b3e6970633db961cf28262ffdd127aa63/dunai/CHANGELOG#L1-L11

I propose to remove those paths from the CHANGELOGs (in both yampa and yampa-test) and decrease the indentation to two spaces. The change in formatting should also be applied to past entries in the CHANGELOGs.