sort: -S/--buffer-size does not support memory percentages %

[zacchiro]

GNU sort v. Rust sort:

$ /usr/bin/sort --buffer-size=50% < /dev/null
$ target/release/coreutils sort --buffer-size=50% < /dev/null
sort: invalid --buffer-size argument '50%'

Relevant excerpts from GNU sort manpage:

       -S, --buffer-size=SIZE
              use SIZE for main memory buffer

[...]

       SIZE may be followed by the following multiplicative suffixes: % 1% of memory, b 1, K 1024 (default), and so on for M, G, T, P, E, Z, Y.

(this could be a good first issue)

[miDeb]

There is an even bigger problem here, which is that sort precomputes data for each line that will be sorted (this makes comparing them faster). Due to that the exact amount of memory usage depends on the number of lines in a chunk (shorter lines -> more lines in a chunk -> more memory usage).
Right now, when you specify a buffer size, the actual memory usage will be less or more than that. I think we should first solve that problem.

[zacchiro]

@miDeb I wasn't aware of that issue, but it looks to me the two can be fixed independently from one another.