Suboptimal Path Data Serialization

[darBis]

Current SVG Parh Data serialization results in output file inflation when it contains lots of path elements. For example small map sheet increased in size from 170 KiB to 190KiB just by loading and writing the SVG throuhg.
Such increase in size is undesired especialy when serving such images over network.

Improve path data serialization in a way similar to inkscape output:

• limit command repetition
• use relative coordinates where applicable
• use special commands for movement in one dimension, if other coordinate does not change