Log Message:
Update to 1.7.1

* Update MASTER_SITES and HOMEPAGE

Changelog:
I've tagged a new release of Ninja, version v1.7.1

(I've also tagged v1.7.0, but don't use that.)

This is the first release after moving the homepage to https://ninja-build.org
and the repo to github.com/ninja-build.

== Release notes
* New feature: Implicit outputs (#989)
  Documented in the manual at https://ninja-build.org/manual.html#ref_outputs
* Output formatting changes
  + in non-interactive mode, print commands when finished, not when started --
    build output is now always preceded by the command that produced it (#999)
  + as a consequence, the default NINJA_STATUS is now "[%f/%t] " and %p
    is percentage of finished edges instead of percentage of started (#1142)
  + for failing commands, print "FAILED: output name" followed by the
    faiilng command on a new line, instead of "FAILED: command" (#1033)

* Several documentation updates

* Minor changes and bugfixes
  + "./" in paths is no longer an error but instead canonicalizes to \ 
nothing
    (#1076)
  + New debugging flag `-d keepdepfile` (#1098)
  + `-w dupbuild=err` now works in subninjas (#1095)
  + Don't loop forever in dry-run mode if the generator rule is dirty (#1069)
  + `msvc_deps_prefix` can now be set per-rule, not just globally (#1043)
  + allow non-ANSI characters in depfiles (#763)
  + `-k 0` now works better with pools (#1017, #1023, #1126)

* `-t browse` changes
  + new --port and --no-browser flags; default to 'all' target (#1112)
  + make tool work if main build file isn't called build.ninja (#1116)

* Windows-specific changes
  + don't crash with deps=msvc if the compiler prints very long include notes
    (#973)

* POSIX-specific changes
  + Clean up build on SIGHUP (#964)
  + subprocesses are now spawned via posix_spawn instead of fork/exec, which
    speeds up builds on some systems (e.g Mac OS X) (#1118)
  + child processes no longer detached from terminal, restoring 1.5.0 behavior
    (#1113)
  + experimentally expose deps=msvc on non-Windows too (#1125)

* Changes to building ninja itself
  + allow bootstrapping ninja itself in an out-of-source build dir (#979)
  + make ninja build on AIX (#1007)
  + ninja's source compiles with MSVC2015 (#1003, #1110, #1130)
  + ninja's source now also compiles with MSVC2008 (!) (#1101)
  + ninja's source builds with libc++ on Linux (#1134)

* Changes to scripts
  + zsh target completion is faster (#1046)
  + bash target completion is faster (#1047)
  + ninja_syntax: don't wrap long words in comments (#1042)
  + ninja_syntax: support implicit outputs