Implement next_date and prev_date

[nakedible]

Add next_date and prev_date algorithms, tests, documentation and benchmarks. Implementation is original but not novel.

[cassioneri]

Have you tried: rd_to_date(date_to_rd(y, m, d) + 1) and rd_to_date(date_to_rd(y, m, d) - 1)? I'm curious. 🙂

[nakedible]

Have you tried: rd_to_date(date_to_rd(y, m, d) + 1) and rd_to_date(date_to_rd(y, m, d) - 1)? I'm curious. 🙂

Yes, I did ;-)

compare_next_date/datealgo
                        time:   [1.0013 ns 1.0091 ns 1.0174 ns]
compare_next_date/datealgo_alt
                        time:   [6.3359 ns 6.3447 ns 6.3541 ns]
compare_next_date/chrono
                        time:   [2.0256 ns 2.0483 ns 2.0710 ns]
compare_next_date/time  time:   [2.1835 ns 2.1888 ns 2.1947 ns]

compare_prev_date/datealgo
                        time:   [963.39 ps 970.16 ps 977.29 ps]
compare_prev_date/datealgo_alt
                        time:   [5.9197 ns 5.9297 ns 5.9404 ns]
compare_prev_date/chrono
                        time:   [2.2530 ns 2.2700 ns 2.2873 ns]
compare_prev_date/time  time:   [2.1307 ns 2.1463 ns 2.1617 ns]

https://github.com/nakedible/datealgo-rs/pull/33/files#diff-8a5132136b7f8e663ead5995baf0fcebd03e79aca4d81f823bad1e403d391bf5R146-R156