* install.md, install-manual.md, and easy-install.md had a lot of
redundancy. Rework them so the common prefix and suffix are in
install.md and it's clear when to navigate back and forth. This
removes from very stale references to prep.sh and cameras.sql in
install-manual.md (which never should have mentioned these scripts
anyway).
* remove all the SAMPLE_MEDIA_DIR, SAMPLE_FILE_DIR, and
SAMPLE_FILE_PATH stuff from the scripts. This was too complicated
(one variable will suffice) and inconsistent in terminology (a
couple "samples dir" occurrences slipped through review; they
should have been "sample file dir"). It also wasn't really useful
enough because the procedure for a mount point is manual anyway,
and because some installs will have multiple sample file dirs
anyway.
* in the mount point procedure, fix the paths to be consistent. Also
describe the "nofail" and "Requires=" config I have on my machine.
* fix some incorrect info about how to use "moonfire-nvr config" and
describe "flush_if_sec".
* upgrade min required rust to 1.21; crossbeam-deque requires the
ord_max_min feature, apparently stabilized in this version.
* use "make --jobs=2" to build ffmpeg so it goes faster.
https://docs.travis-ci.com/user/reference/overview/ says there are 2
cores available.
* upgrade minimum required Rust from 1.17 to 1.20; reffers 0.4.2
apparently uses std::mem::ManuallyDrop, introduced in 1.20
* install ffmpeg from source (requiring sudo access) rather than using
the ancient one from Ubuntu Trusty to meet the minimum version
requirements specified in ffmpeg/build.rs.