rs: avoid panic in day 20 (debug mode only, release is fine)
Merge branch 'main' of git.sr.ht:~cdv/aoc-2020 into main
rs: need debug symbols in release mode
Attempt to use huge pages for day 15

On this machine, I don't have enough hugepages to allocate it all with
hugepages unfortunately, so this doesn't represent any performance gain.
c: fix downloader for when year is $CURRENT_YEAR and day > 25
c: day 23, use mmap and hugepages for better cache accesses
rs: rewrite rust to be contained in one binary

All the following are supported:
* download and save inputs using hyper/tokio
* run all or some of the solutions
* run the solutions in parallel using rayon
hs: day 24, Pair should be strict
rs: O(log(n)) mod exponent
rs: cleanup day 25
rs: day 25

Merry Christmas!

Probably a faster version involving mod inverse and similar, but this is
only a few ms.
hs: don't error on unimplemented day 25
hs: don't error on not yet implemented days