android-config: Disable libxml2 for user build, use long clang names
Isolate std::future when NOTHREADS is defined and build without SOCK_{NONBLOCK, CLOEXEC}
nghttpx: Android specific hack for special files for logging

Android lacks /dev/stderr, so directly use /proc/self/fd/2 as default
errorlog-file.  Android does not like O_APPEND for /proc/self/fd/1 and
/proc/self/fd/2, so omit the flag for these paths.
doc: Add building-android-binary document