OrderedIntervalList

[patsak]

resolve #41

[coveralls]

Pull Request Test Coverage Report for Build 155

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+14.0%) to 62.651%

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Totals
Change from base Build 152:	14.0%
Covered Lines:	75
Relevant Lines:	128

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 185

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+26.5%) to 75.185%

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Totals
Change from base Build 152:	26.5%
Covered Lines:	126
Relevant Lines:	178

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💛 - Coveralls

[Eenae]

Also, insert and append functions have O(n) on-chain complexity. In practice it'll kick in only in case of long contiguous ranges of holes inside list.
I think it could be optimized by building a linked list using pointer machine over storage. It'll require quite heavy rewrite.
@k06a what do you think should we spend some time now optimizing it?

[k06a]

Arguments should not have underscore prefix anymore, see OpenZeppelin 2.0 notation.