git ignore build results in their new location
Move `require`s above modules that use them

In preparation for splitting those modules into separate files and combining them together again in the Makefile
Write HTMLTablesDocumentBuilder
Change Makefile variable names to lower case

for readability, and as recommended in the Make manual at http://www.gnu.org/software/make/manual/make.html#Using-Variables
change Makefile to support splitting header.rb into multiple files

The parts of header.rb that don’t have to be at the very top of the file can be moved into individual files within the folder `build/src/common/`.
Change .gitignore to a whitelist

Following the template of http://stackoverflow.com/a/5250314/578288 (“Using .gitignore to ignore everything but specific directories”)
Split header.rb into many files in common/

Leaving in header.rb the part of the file that actually has to be at the head