Revert "remove Sampling, which has been irrelevant for quite a while."

This reverts commit 684183bd9e3f9cfdeec96f1f4df5ad2506f4dc23.
correct the url for Sampling.jl
Tag SymPy v0.2.15
Merge pull request #1130 from jverzani/pull-request/c8e2ea06

Tag SymPy v0.2.15
Tag MultivariateStats v0.1.1
Merge branch 'metadata-v2' of https://github.com/JuliaLang/METADATA.jl into metadata-v2
Tag DimensionalityReduction v0.1.2
Tag RandomMatrices v0.0.1
Merge pull request #1131 from jiahao/pull-request/463c3ba7

Tag RandomMatrices v0.0.1
Tag Distributions v0.5.4
Merge branch 'metadata-v2' of https://github.com/JuliaLang/METADATA.jl into metadata-v2
Tag MLBase v0.3.6
Tag StatsBase v0.6.2
Tag MLBase v0.4.0
Tag StatsBase v0.6.3
Tag MLBase v0.4.1
Tag MLBase v0.4.2
Tag MLBase v0.5.0
Tag GradientBoost v0.0.1
Merge pull request #1133 from svs14/metadata-v2

Tag GradientBoost v0.0.1