help: use 'churn' instead of 'color' as an example extension The 'color' extensions is now deprecated.

config: suggest the 'ui.color' instead of the 'color' extension The extensions is deprecated now so we should offer the core way to handle color instead.

color: update main documentation Now that the feature no longer lives in the extension, we document it in the help of the core config. This include the new 'ui.color' option introduced in the previous changesets. As a result the color extensions can now be deprecated. This is a documentation patch only; color is still disabled by default.

pager: drop the 'color' dependant code The 'color' implementation is in core and no longer wrap '_runcommand'. We drop the extra complexity.

color: cleanup 'debugcolor' logic Now that style are carried by the 'ui' object, we no longer need complicated logic to restore the original style. We just need to copy the 'ui' and work on the copied version.

color: move 'debugcolor' into the 'debugcommands' modules This is the last bits we needed to move out of the extensions. 'hgext/color.py' now only contains logic to changes the default color behavior to 'auto'. However, more cleanups are on the way and we need to document the new config directly in core.