ui: support declaring path push urls as sub-options Power users often want to apply per-path configuration options. For example, they may want to declare an alternate URL for push operations or declare a revset of revisions to push when `hg push` is used (as opposed to attempting to push all revisions by default). This patch establishes the use of sub-options (config options with ":" in the name) to declare additional behavior for paths. New sub-options are declared by using the new ``@ui.pathsuboption`` decorator. This decorator serves multiple purposes: * Declaring which sub-options are registered * Declaring how a sub-option maps to an attribute on ``path`` instances (this is needed to `hg paths` can render sub-options and values properly) * Validation and normalization of config options to attribute values * Allows extensions to declare new sub-options without monkeypatching * Allows extensions to overwrite built-in behavior for sub-option handling As convenient as the new option registration decorator is, extensions (and even core functionality) may still need an additional hook point to perform finalization of path instances. For example, they may wish to validate that multiple options/attributes aren't conflicting with each other. This hook point could be added later, if needed. To prove this new functionality works, we implement the "pushurl" path sub-option. This option declares the URL that `hg push` should use by default. We require that "pushurl" is an actual URL. This requirement might be controversial and could be dropped if there is opposition. However, objectors should read the complicated code in ui.path.__init__ and commands.push for resolving non-URL values before making a judgement. We also don't allow #fragment in the URLs. I intend to introduce a ":pushrev" (or similar) option to define a revset to control which revisions are pushed when "-r <rev>" isn't passed into `hg push`. This is much more powerful than #fragment and I don't think #fragment is useful enough to continue supporting. The [paths] section of the "config" help page has been updated significantly. `hg paths` has been taught to display path sub-options. The docs mention that "default-push" is now deprecated. However, there are several references to it that need to be cleaned up. A large part of this is converting more consumers to the new paths API. This will happen naturally as more path sub-options are added and more and more components need to access them.