add --in-place flag

[tennox]

See #191 for details

I gave it a shot. Tell me what you think :)

I've also parameterized the tests so the flag is also tested for the same cases.

I did some hyperfine benchmarks to make sure performance isn't severely degraded and it's mostly the same:

$ hyperfine -N -w1 -p 'cp source.txt test.txt' "/home/manu/dev/stuff/sd/target/debug/sd foo bar test.txt" "/home/manu/dev/stuff/sd/target/debug/sd --no-swap foo bar test.txt"

(tried with input sizes: 10B, 1KB, 10MB and containing foo on each line)

[CosmicHorrorDev]

As a heads up I'll be putting this on the back burner until after the v0.8.0 release. I'm focusing on getting existing functionality fixed up while saving new features for later

[PeterlitsZo]

LGTM

[ThinkChaos]

_{(Just a random user's opinion, don't take this with authority)}

I think taking the naming from sed would make this more easily discoverable, and is more easily understandable IMO:

-i[SUFFIX], --in-place[=SUFFIX]
    edit files in place (makes backup if SUFFIX supplied)

I'm not a fan of -i[SUFFIX] given -ijkl means -i -j -k -l, but -i=suffix could be nice.

[tennox]

Merged latest master & reworked the implementation accordingly (which made it a good bit simpler :+1: )

[tennox]

I think taking the naming from sed would make this more easily discoverable, and is more easily understandable IMO:

-i[SUFFIX], --in-place[=SUFFIX]
    edit files in place (makes backup if SUFFIX supplied)

@ThinkChaos thanks, I took (part of) your suggestion, and renamed to --in-place (no short flag / custom suffix implemented).