svg: Add missing inline qualifiers.

This fixes multiply defined symbol errors when using the
svg header in multiple translation units.
svg: Add missing translation/scale for EllipticalArc.
vd2svg: Mark functions defined in header as inline, to avoid linker errors
when including the header from multiple compilation units.
vd2svg: Color-code more edge types.
kdtree: Don't try to dereference "rect_" if not initialized
(i.e. root_ == NULL).
Solver: initialize variables in constructor.
halfedge diagram: mark appropriate methods as const.
cmake: Comment out hard-coded build type in CMakeFile.txt

Build type is usually chosen by invoking something like "cmake -DCMAKE_RELEASE_TYPE=Release"
at configuration time.
cmake: Modify quotation marks as to not generate any warnings.
Fix medial-axis filter discarding skeleton edges at very
pointy polygon corners.

Previously, the filter would threshold on the absolute value of
the cosine, thus regarding LINESITES with small interior
angle as parallel (because edges with nearly opposing directions have
a cosine close to -1).
Decrease epsilon in quad-float chop method.
Numerically stabilize detection of parallel line / line sites.
Increase tolerance when identifying parallel edges.
Try parallel solver if determinant of LLL solver is close to zero.
Merge pull request #11 from mmassing/master

Various stabilization + some compile/linking fixes