add man pages for solve*

build a serious test suite

build generic skipping tool for arithmetic progressions
find good progressions given polynomial (e.g., mod 91 for cube)

have programs check carefully for overflow, abort if overflow is possible

add sortedpq_skip() to jump to new min
reduce sortedpq_next() overhead; buffer results
consider other prioq implementations
work around compiler stupidities in alignment, scheduling, etc.

reduce code duplication between sortedpq, sortedpp
reduce code duplication among solve*
extract other common routines

handle memory allocation more sensibly
rewrite from scratch
