optimize build.ninja depfiles

We don't need the extra DEPFILE / DEPFILE_UNQUOTED variable since we can
just construct that from within the build.ninja.

For meson's rationale for DEPFILE_UNQUOTED see commit
5ca37e7961ac2068382c36424c3f972ed0a9a105.  The rationale for DEPFILE,
however, I'm unable to discern.  It seems to have been the original
implementation, and I'm not sure if there are any benefits.
optimize build.ninja rules

- reduce duplication of ARGS by generating a rule per target
optimize build.ninja order deps

- dedup order deps
- create a phony target per build target to group order deps (credit for
  this idea to Andres Freund!)
add status title and favicon
remove unused getopt.h include
fix handling of objects: in both_libraries()
remove margin for thin screens
fix status page style with light theme
link to status page on website and readme
add implementation status page to website
update meson-docs wrap
add dump_signatures subcommand

This subcommand dumps type information for all recognized functions and
methods, including module functions.
comment out test depending on dependency('boost')
add support for -Darray=['a', 'b', 'c'] style
re-allow options to be set with empty values
13606583 — illiliti 6 days ago
refactor fs_copy_link

use fstat to get buffer size instead of busy looping readlink
b5ec9dbe — illiliti 6 days ago
use proper return type for readlink
9275700e — illiliti 6 days ago
null-terminate readlink buffer

readlink does not null-terminate the buffer. do it manually to avoid
creating corrupted symlinks.
add fuzzing run targets
fix a meson warning