This closes #135

This makes it easy to build WF for ARMv7, e.g. the Raspberry Pi.

part of #135

Fixes issue 125

This ensures outside application builds will succeed when including the
writefreely pkg.

Ref T613

This also moves development instructions to documentation repo.

Using xgo comes with its own gomod-related issues. So let's see if this
fixes the build issue mentioned in the previous commit.

This will hopefully fix Travis errors:

/home/travis/.gimme/versions/go1.11.7.linux.amd64/pkg/tool/linux_amd64/link: running gcc failed: exit status 1
/usr/bin/ld: /tmp/go-link-810454258/000020.o: unrecognized relocation (0x2a) in section `.text'
/usr/bin/ld: final link failed: Bad value

This fixes an error: undefined: Asset

Based on @sheenobu's work on #58

Supports creating a build without SQLite support compiled in.

This adds a new `sqlite` build tag that you should include only if you
want SQLite3 support built in. Both `make run` and `make release` create
builds with SQLite included.

This includes schema.sql and sqlite.sql in the release binary, so they
no longer need to be included in the release archives. This reduces the
number of files extracted, but otherwise leaves all functionality as it
was -- especially the --init-db flag.

Ref T536

(not "darwin")

Ref T529

Part of T529

- "v" should not be part of the version (softwareVer variable is used
  in other places)
- formatting

Sets value of softwareVer during build

This eliminates an external dependency needed for install, and ensures
the app can run on Windows.

- Fixes make clean
- Changes make to make ui
- Generates keys on make install
- Adds make run, make build