Define empty string variable KICAD_BRANCH_NAME that can be used as an
optional version string element. When git is used to build the version
string, this variable is set to the git branch name. It can also be
defined at configuration time as an optional string appended to the
$KICAD_VERSION variable.
Define empty string variable KICAD_VERSION_EXTRA that can be set by
the user at configuration.
The variables KICAD_BRANCH_NAME and KICAD_VERSION_EXTRA are only
appended to KICAD_VERSION if they are set. Otherwise, only KICAD_VERSION
is uses as the version string.
Update the developer building from source document to reflect the changes.
Add KiCadVersion.cmake to set the build version and branch name.
Update WriteVersionHeader.cmake to include KiCadVersion.cmake to set
the defaults in case no .git directory is found.
Wayne Stambaugh