Add travis CI, linter

.travis.yml

@@ -0,0 +1,9 @@
+language: python
+python:
+  - "2.7"
+  - "3.4"
+  - "3.5"
+script:
+  - pip install sphinx
+  - python misc/lint.py
+  - make html

misc/lint.py

@@ -0,0 +1,39 @@
+#!/usr/bin/env python3
+"""Check for tabs and trailing whitespace in text files in all subdirs.
+
+Any other automatic checks should be in this file too.
+"""
+
+import os
+import sys
+
+text_extensions = ('rst', 'md', 'txt', 'html', 'css', 'js')
+
+
+def lint():
+    """Run linters on all files, print problem files."""
+    print('Checking for tabs or trailing whitespace...')
+    failed = False
+    for root, _, files in os.walk('.'):
+        for f in files:
+            fname = os.path.join(root, f)
+            if '_build' in fname or not any(
+                    fname.endswith(ext) for ext in text_extensions):
+                continue
+            with open(fname, encoding='utf-8') as fh:
+                if '\t' in fh.read():
+                    failed = True
+                    print('ERROR:  tabs found in {}'.format(fname))
+                if any(line.replace('\n', '') != line.rstrip()
+                       for line in fh.readlines()):
+                    failed = True
+                    print('ERROR:  trailing whitespace in {}'.format(fname))
+    if failed:
+        print('Use your text editor to convert tabs to spaces '
+              'or trim trailing whitespace with minimal effort.')
+        sys.exit(failed)
+    print('All files are OK')
+
+
+if __name__ == '__main__':
+    lint()