Update travis_notes and move to tools folder

doc/travis_notes.txt → tools/travis_notes.txt

@@ -1,5 +1,6 @@
 
-- Use http://yaml-online-parser.appspot.com/ to make sure it is valid yaml.
+- Use http://yaml-online-parser.appspot.com/ to make sure
+the yaml file is valid.
   http://lint.travis-ci.org/ is recommended elsewhere but does not give helpful
   error reports.
 - Make sure all of your "-" lines start on the same column
@@ -13,9 +14,11 @@
      set -ex
    ```
 
-- Use `travis_retry` before a command to have it try several times before
-failing (useful for installing from third party sources).  Note that this
-command is not available within a bash script.
+- Use the `retry` bash function from `before_install.sh` before a command to have it try 3 times before
+failing (useful for installing from third party sources).
+- Use the `section` function to start a folded section of the script.
+Section names must have underscores or dots instead of spaces and must be
+accompanied by a corresponding `section_end` call.
 - Feel free to cancel a build rather than waiting for it to go to completion
   if you have made a change to that branch.
 - A VM with 64bit Ubuntu 12.04 is a huge help for debugging.