cmdutil: drop redundant import of merge module

annotate: add support for template keywords and functions depending on ctx

formatter: unblock storing fctx as a template resource To keep templateformatter._renderitem() simple, a repo instance is looked through ctx if available. This is probably good for future subrepo support where ctx.repo() may be different from the global repo.

templater: process mapping dict by resource callables A resource item is a callable, so let's make it look up a resource object by itself.

templater: convert resources to a table of callables for future extension I'm going to add a full templating support to the annotate command. As the annotate is a filectx-oriented command, we'll need a way to look up a ctx from a bounded fctx only when necessary. This is the minimal change to support that. I'm thinking of defining a proper interface to look up template resources to fix other issues, but that isn't ready yet. (Changes from V1: just updated tests and patch descriptions.)

merge with stable

hgweb: convert an assert to a ProgrammingError Because assert may get optimized away. Differential Revision: https://phab.mercurial-scm.org/D2882