build and lint the UI in travis-ci

This is a separate item in the matrix, so it doesn't go through this for
each of the three Rust versions.

ci/install-ffmpeg.sh

@@ -0,0 +1,13 @@
+#!/bin/bash -e
+if [ ! -f ffmpeg-${FFMPEG_VERSION}/configure ]; then
+  wget https://ffmpeg.org/releases/ffmpeg-${FFMPEG_VERSION}.tar.xz
+  tar xf ffmpeg-${FFMPEG_VERSION}.tar.xz
+fi
+cd ffmpeg-${FFMPEG_VERSION}
+./configure --enable-shared
+make --jobs=2
+sudo make install --jobs=2
+sudo ldconfig
+
+# The build log varies with each invocation; remove it to improve cachability.
+rm -f ffbuild/config.log

ci/script-rust.sh

@@ -0,0 +1,6 @@
+#!/bin/bash -e
+cargo build --all
+cargo test --all
+if [ "$TRAVIS_RUST_VERSION" = nightly ]; then
+  cargo bench --all
+fi