add unit tests for alpha unblending
move unit tests into pdf_decanter package
add some docstrings
inline trivial adjusted_rect() wrapper
update README w.r.t. cache location
ignore experiments and .DS_Store
extract method unblend_alpha_1d
don't transpose array in unblend_alpha_1d
use integer computations for alpha unblending
improved cache handling (separate options for use & creation)