Measure CPU Time not Wall Clock Time

Changes:

• Spiral's seconds_spent field now counts seconds of CPU time spent processing the spiral, not wall-clock time (the former is a more faithful reflection of processing complexity when compared with others on the same system).
• Marked sxbp_resize_spiral() as deprecated from the Public library interface.
• Amend directory and instructions to easily facilitate out-of-source builds.

Breaking file format release

BREAKING RELEASE!

Improvements:

• 16-bit version identifiers in library and file format
• 32-bit friendly code
• storing of time spent generating a spiral (and the accuracy of this figure) in file

More liberally-licensed, now with Doxygen documentation

• Software license changed to MPL-2.0
• Doxygen documentation added

Rename

This version update renames the library in source from libsaxbospiral to libsxbp

Perfection Threshold bugfix

Fix bug where wrong type was used for perfection_threshold argument
This was an int, but should have been the unsigned library type sxbp_length_t

No compulsory Dependencies!

This version sees the dependency on libpng made optional (by making PNG output optional)
By default, PNG support is enabled if libpng can be found or disabled if it cannot.
By using the CMake variable SAXBOSPIRAL_PNG_SUPPORT one can optionally force enable or disable this.
In C code, you can check the library constant bool SXBP_PNG_SUPPORT. If it is true then PNG output is
supported, otherwise it is not.

Also, this is the first tag to be signed with my PGP key, hurrah!

Render Backends Refactor

v0.21.0

Render Backends Refactor

Cleanup and Improvements

• Removed SXBP_DEBUG symbol
• Added assertions
• Library headers now are installed under version-specific locations to allow different versions of saxbospiral to exist together at the same time.

That which has been open-sourced

Go forth my child! Do me proud!

Going Solo

Library and command-line program have now been completely separated.