adg: corrected some gir annotation
build: including gschemas.compiled in dist

gschemas.compiled *must* not depend on the system provided schema: it
must be set to a bare minimum and included just to avoid crashes on
Windows due to the missing GtkFileChooser schema.
build: use DLLDIR instead of guessed USRDIR

The GObject prefix is now only used for picking up the Windows DLLs, so
manifesting it in the code. The new variable is precious, so there is a
way to use a custom path at configure time. In any case, all the DLLs
must reside inside the same directory.
adg: removed AdgPattern

cairo-gobject yet wraps cairo_pattern_t, so there is no need to
duplicate it (and makes bindings life easier).
cpml: protect cpml_pair_copy() against NULL

Enhanced cpml_pair_copy() to make adg_pair_copy() redundant.
Moved AdgPair to CpmlPair

AdgPair was a GBoxed wrapper around CpmlPair. This complicates bindings
(lua-lgi based) because CpmlPair and AdgPair APIs must be able to accept
both forms (hence must provide an *alias* feature).

Avoid the problem in the first place by only using CpmlPair and drop
AdgPair. This means CPML now depends on GObject.
Moved AdgPrimitive to CpmlPrimitive
Moved AdgSegment to CpmlSegment
doc: updated doap record
adg: use cairo_matrix_t instead of AdgMatrix

An alias such as the old AdgMatrix creates problems with bindings.
Removed the alias and directly used cairo_matrix_t instead. Provided a
backward compatibility wrapper that implements a GBoxed around
cairo_matrix_t in the way cairo would implement it (cairo-gobject, for
some unknown reason, did not wrap it: see [1] for details).

[1] http://lists.cairographics.org/archives/cairo/2013-March/024104.html
doc: updated copyright