Use a variable instead of a hard coded path

Applies to items in the build element
Fixed build-directory

It was hard coded, change it to use value from config file if defined
Tweak fix to config.xsl
Fixed typo in error message
Rearranged some settings and reworked directory paths

Separated the various build-related files from the documentation output.
Reorganized some elements to put common definitions in the main
configuration file.
corrections and enhancements to element descriptions
Latest topic updates, including one new topic