[PULL REQUEST] Make default pages configurable

I proposed this change a while ago, but it didn't seem to get much
attention. Please tell me if I'm doing something wrong.

It would be nice to be able to configure the default page to use for the
root site and repositories. For example, it might make more sense to
have "about" or "tree" as the default landing page for certain repos,
instead of the default "summary".

This patch introduces the following configuration settings:
- "root-default-page": sets the default page for the root site
  (defaults to "repolist")
- "repo.default-page": sets the default page for individual repos
  (defaults to "summary")
- "default-page": global default value for "repo.default-page"

The following accessory changes were required to make this work:
- the "index" tab link on root pages and the "summary" tab link on repo
  pages now explicitly point to their respective targets instead of
  pointing to the site/repo root
- trying to access the "about" page on a repository without one results
  in being redirected to the "summary" page explicitly

The following changes since commit 8fc0c81bbbed21ee30e8a48b2ab1066a029b7b32:

  git: update to v2.23.0 (2019-10-25 11:40:17 +0200)

are available in the Git repository at:

  https://git.monade.li/cgit

for you to fetch changes up to 1431881898ba6044bfd3ae12cc45fb5fcadf80c7:

  Make default pages configurable (2019-12-09 19:38:14 +0100)

----------------------------------------------------------------
Na?m Favier (1):
      Make default pages configurable

 cgit.c        | 10 ++++++++++
 cgit.h        |  3 +++
 cgitrc.5.txt  | 14 ++++++++++++++
 cmd.c         | 18 +++++++++---------
 ui-repolist.c |  2 +-
 ui-shared.c   | 12 +++++++++---
 ui-shared.h   |  2 ++
 7 files changed, 48 insertions(+), 13 deletions(-)