Add lint for filenames

We have established a pattern of Alpha and underscores for filenames.
This adds a hook to keep this pattern going. Also fixes a misnamed file
I found in the process.

Resolves #456

.github/lint-filename.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+set -e
+
+SCRIPT_PATH=$( cd "$(dirname "${BASH_SOURCE[0]}")" ; pwd -P )
+GO_REGEX="^[a-zA-Z_]+\.go$"
+
+find  "$SCRIPT_PATH/.." -name "*.go" | while read fullpath; do
+  filename=$(basename -- "$fullpath")
+
+  if ! [[ $filename =~ $GO_REGEX ]]; then
+      echo "$filename is not a valid filename for Go code, only alpha and underscores are supported"
+      exit 1
+  fi
+done

.travis.yml

@@ -26,3 +26,4 @@ script:
   - bash .github/assert-contributors.sh
   - bash .github/lint-disallowed-functions-in-library.sh
   - bash .github/lint-commit-message.sh
+  - bash .github/lint-filename.sh