Add support for MOI.AbsoluteGapTolerance and MOI.RelativeGapTolerance #130

Job	Run time
Julia 1.6 - ubuntu-latest - x64 - pull_request	12m 26s
Julia 1.6 - macOS-latest - x64 - pull_request	4m 27s
Julia 1.6 - windows-latest - x64 - pull_request	19m 58s
Julia 1 - ubuntu-latest - x64 - pull_request	11m 56s
Julia 1 - macOS-latest - x64 - pull_request	3m 14s
Julia 1 - windows-latest - x64 - pull_request	12m 11s
Julia 1.6 - ubuntu-latest - x86 - pull_request	14m 31s
	1h 18m 43s

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