Fix WrapWords excessive memory utilization

[horkhe]

When feeding production data to this library we discovered that function WordWrap had O(n*n) memory complexity, that resulted in huge amounts of memory allocated when processing even relatively small strings. We are talking Gigabytes that made our production services killed with OOM. This PR implements 2 optimisations:

• Function splitWords was introduced to efficiently break a line into words. Note that unlike original implementation it does not consider empty spaces to be words.
• Function WrapWords was rewritten to be O(n) on memory complexity. A benchmark that comes with this PR shows great improvement:

  BenchmarkWrapString-16
  Before:     1   2490331031 ns/op    2535184104 B/op 50905550 allocs/op
  After:   1652       658098 ns/op        230223 B/op     5176 allocs/op

[horkhe]

@olekukonko any chance to get this PR looked at?

[olekukonko]

@horkhe sorry for the late response, this is wonderful, will take my time to look at this next week so that it can be merged

[olekukonko]

@horkhe can you kindly update your PR and resolve merge conflicts, I Would really like to merge this performance improvement. thank you

[horkhe]

@olekukonko sorry for the late response. I have rebased this PR, please take a look.

[horkhe]

@olekukonko any chance to get this merged?

[horkhe]

@olekukonko any chance to get this merged?

[olekukonko]

@horkhe will look at this this weekend and revert. Thank you for being consistent.

[horkhe]

@olekukonko a friendly reminder.

[horkhe]

Thanks a lot! Could you please also tag the master with v0.0.6, so it can be picked up by go mod.