Add dropWhileEnd, takeWhileEnd, strip

[nmattia]

A few notes:

• I couldn't build the benchmarks, so I haven't added benchmarks for the new functions. However their implementation is very similar to that of other functions so it shouldn't make too big a difference (though I don't know if I should inline strip).
• I don't know how closely Data.ByteString.Char8 is trying to follow the functions on String: for instance, there is no strip function on String. Let me know whether exporting the strip and dropSpace functions is the right thing to do or not (though my motivation for adding dropWhileEnd and takeWhileEnd is to have strip).
• I haven't implemented dropWhileEnd and takeWhileEnd on lazy bytestrings, because (1) I don't know how much sense it makes and (2) I wouldn't know how to do that efficiently, for some definition of efficiently.

[nmattia]

Note: this should address #19.

[bgamari]

@dcoutts, it seems like this would be rather nice to have.

[typesanitizer]

I haven't implemented dropWhileEnd and takeWhileEnd on lazy bytestrings, because (1) I don't know how much sense it makes and (2) I wouldn't know how to do that efficiently, for some definition of efficiently.

Lazy Text has both dropWhileEnd and takeWhileEnd. Since the chunked representations of lazy Text and lazy ByteString are very similar, I think it makes sense for bytestring to provide the corresponding functions. Similarly, lazy Text also has a strip function, so maybe it should be added too.

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The strip implementation in the PR uses dropWhile isSpace which could be replaced by dropSpace (there is a rewrite rule for this so it shouldn't matter in practice). There is also a dropSpaceEnd function commented out (I'm not sure why it is commented out though) which could be used here.

[hvr]

A related PR is #155 adding findIndexEnd

[nmattia]

What should we do here? This has been open for 2 years and I'd like to delete my bytestring fork

[nmattia]

Gentle ping

[nmattia]

@dcoutts ping!

[relrod]

+1 for these; anything I (as a community member) could do to help move this along?
/cc @dcoutts

[nmattia]

@hvr @dcoutts ping!

[Bodigrim]

Looks good to me. We can raise a separate issue to discuss an implementation of {take,drop}WhileEnd on lazy ByteStrings, but I do not think this should be a blocker for merging. CC @cartazio

[Bodigrim]

@nmattia could you please update changelog?

[nmattia]

@Bodigrim done, apologies about the delay!

[nmattia]

Fixed conflicts, shall we merge?

[sjakobi]

@nmattia We're currently preparing a bug fix release for GHC 8.8.4 and 8.10.2: #235

I'd like to merge this very soon after that release.

@hsyl20, @bgamari Would you like to review?

[hsyl20]

LGTM and tests pass locally too. Thanks @nmattia!

[nmattia]

Updated changelog! @sjakobi anything else I can do?

[Bodigrim]

@nmattia I'll merge this, once we get 0.10.10.1 out (hopefully today).

[Bodigrim]

Merged, thanks for your patience!