PDF and SVG support added to OASA

In the newest versions of OASA, I have added the possibility to create images not only in PNG, but also in SVG and PDF.
This functionality comes for free as a courtesy of the Cairo library and gives the user the possibility to create output much more suitable for printing.
Here is a small example code showing how to create a PDF export:

from oasa import smiles, cairo_out
mol = smiles.text_to_mol( "Oc1ccc(N)cc1Cl")
mol.normalize_bond_length( 30)
mol.remove_unimportant_hydrogens()
cairo_out.mol_to_cairo( mol, "example.pdf", format="pdf")

The output looks like this (of course, this is rendered to PNG, the PDF can be found here):

(Because SMILES was used as input, OASA generates the 2D structure for you.)
For SVG, just replace "pdf" with "svg" in the example above.
The cairo_out.mol_to_cairo function has many keyword arguments that allows for changing of almost every aspect of the output. For example, the following adds hydrogen symbols to hetero-atoms and changes the line width for bonds.

cairo_out.mol_to_cairo( mol, "example.svg", format="svg",
                     show_hydrogens_on_hetero=True,
                     line_width=2)

The output now looks like this (again in PNG, the SVG can be found here):



One big advantage of the SVG generated by Cairo is that all text is converted to curves. This means that the output will look the same on every machine, regardless of installed fonts.