Install using standard Perl mechanisms

[jonchang]

This series of patches uses Module::Install to automatically install VelvetOptimiser to standard locations, removing the need to move the module and script by hand to the correct places.

Commit a762a08 also improves cross-platform portability.

[biocyberman]

Total silence from the maintainer @tseemann? "Yes" or "No", and some "Why" will show that you care about your program.

[tseemann]

@biocyberman the primary maintainer is @Slugger70 . our jobs do not provide salary to maintain tools forever unfortunately, especially superseded ones. such is the nature of the 12 month contract in Australian academia.

[biocyberman]

@tseemann It's always easier to criticize a problem than actually to fix it. I was probably frustrated with the silence about this PR after some years, therefore the comment was a bit harsh.