add CI to set the stage for running fontbakery (#38)

- fontmake cannot be run yet, it errors (https://github.com/chrismsimpson/Metropolis/pull/35/commits/1b143bec257e5c2d37d760f4eb83db4219e88c75 seems to indicate that the following will fix the build issues: adding a Light[700] bracket layer for each of the glyphs that were causing fontmake builds to fail: the cent and the dollar on both the Regular and the Italic)
- subsequent steps are commented out so that they can be enabled progressively in subsequent PRs

.travis.yml

@@ -0,0 +1,8 @@
+language: python
+
+install:
+  - pip install --upgrade pip
+  - pip install -r Sources/requirements.txt
+
+script:
+- ./Sources/build.sh

Sources/build.sh

@@ -0,0 +1,35 @@
+#!/bin/bash
+set -ex
+DIR="$(dirname "${BASH_SOURCE[0]}")"
+BASEDIR="$DIR/.."
+cd "$BASEDIR"
+  OUTPUT_DIR="$BASEDIR/build_output"
+  SOURCE_DIR="$BASEDIR/Sources"
+
+  rm -rf $OUTPUT_DIR
+
+  # for src in $SOURCE_DIR/*.glyphs
+  # do
+  #   fontmake -g $src -o ttf -i --output-dir $OUTPUT_DIR/
+  # done
+
+  # for font in $OUTPUT_DIR/*.ttf
+  # do
+  #   gftools fix-nonhinting $font $font
+  #   gftools fix-dsig $font --autofix
+  # done
+
+  # Cleanup gftools mess:
+  # rm $OUTPUT_DIR/*-backup-fonttools-prep-gasp.ttf
+
+  # cp METADATA.pb $OUTPUT_DIR
+  # cp DESCRIPTION.*.html $OUTPUT_DIR
+
+  # export OPTIONS="--no-progress"
+  # export OPTIONS="$OPTIONS --exclude-checkid /check/ftxvalidator" # We lack this on Travis.
+  # export OPTIONS="$OPTIONS --exclude-checkid /check/metadata" # Comment this out after creating a METADATA.pb file.
+  # export OPTIONS="$OPTIONS --exclude-checkid /check/description" # Comment this out after creating a DESCRIPTION.en_us.html file.
+  # export OPTIONS="$OPTIONS --exclude-checkid /check/varfont" # Comment this out when making a variable font.
+  # export OPTIONS="$OPTIONS --loglevel INFO --ghmarkdown Fontbakery-check-results.md"
+  # fontbakery check-googlefonts $OPTIONS $OUTPUT_DIR/*.ttf
+cd -

Sources/requirements.txt

@@ -0,0 +1,3 @@
+git+https://github.com/googlefonts/fontbakery
+git+https://github.com/googlefonts/gftools
+fontmake