[parity-util-mem] migrate code to 2018 edition

[iamsauravsharma]

Migrate parity-util-mem to 2018 edition
Part of #143

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[iamsauravsharma]

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[cheme]

@iamsauravsharma , thanks for going through it.
Things seems fine to me, except the ci was lacking a use case, I updated things in this commit : cheme@d65d43e , see if you can add it to your PR (I think it should be removed, but still updated it).

[dvdplm]

(I think it should be removed, but still updated it).

Not sure I understand what you mean here: what is it that should be removed?

[cheme]

get_malloc_size_src.sh and slim_malloc_size_of.patch (the comment with github commit to servo commit should be enough). It was probably me that wanted to keep it in the first place, but time passing I realize it does not really have any value.

[ordian]

Let's remove get_malloc_size_src.sh and slim_malloc_size_of.patch and we're good to go.