STYLE: added dxf_style_free().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
(#21) Cascade down Makefile.am files - no functional impact

The 'doc/refguides/Rxx' subdirectories have been included directly in the main
Makefile.am, although there exists a defined Makefile.am in the 'doc/'
subdirectory already. The commit creates a nicely cascaded 'SUBDIR' inclusion
in the different Makefile.am files. Note that this does not alter any
behaviour.
(#21) Update refguide directories to use Makefile.am

Updated the refguide directories to use autotools conformant Makefile.am. This
way all possible targets from parents will work and not create an error like
the 'install' target did before. This patch will create a HTML version of the
refguide DocBook files, but it will *not* install these files upon a 'make
install'.
STYLE: added members to DxfStyle struct.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
STYLE: added dxf_style_write().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
Merge pull request #22 from dinkel/fix-make-install-refguides

Fix make install refguides