Switch from SSH to HTTPS cloning
Fix build problems for ubuntu 14.04
Polish text
Simplifying Markdown files even further.

1. Tidied up wording in README.md.
2. Took background and design discussion out of CUSTOMIZATION.md and put it into DESIGN.md.
Merging #1 from @DamienIrving manually
Merging #26 manually
Adding instructions to install the Python YAML module (resolves #15)
Merging in changes from gh-pages
Merge pull request #35 from gvwilson/tidying-up-wording

Simplifying Markdown files even further.