FitMC and as.alienData

[KevCaz]

This PR includes :

• fitMC : the Matching-Centrality as described in Rohr's papers (AmNat 2014 ProceedingsB 2016) is implemented. Note that I am still thinking about the best strategy to test it properly,
• as.alienData: a generic function to convert various objects (i.e data.frame, adjacency matrix and igraph) to our alienData class; These functions are tested,
• tests included within test-nichemodel.Rare now fixed,
• I have also reviewed the simulated data in minimalEx.R (see the test/testthat) to get all species connected (previously some species were not connected which triggered warnings).

[codecov-io]

Codecov Report

Merging #35 into master will increase coverage by 5.06%. The diff coverage is 39.05%.

@@            Coverage Diff             @@
##           master      #35      +/-   ##
==========================================
+ Coverage   49.21%   54.28%   +5.06%     
==========================================
  Files           6       11       +5     
  Lines         256      420     +164     
==========================================
+ Hits          126      228     +102     
- Misses        130      192      +62

Impacted Files	Coverage Δ
src/getNull.cpp	12.5% <ø> (ø)	:arrow_up:
src/webFromNicheModel.cpp	100% <ø> (+97.67%)	:arrow_up:
R/getConnectance.R	0% <0%> (ø)
R/alienPredict.R	0% <0%> (ø)
R/getEdgesList.R	100% <100%> (ø)
R/alienData.R	90.9% <100%> (-0.84%)	:arrow_down:
R/getAdjacencyMatrix.R	100% <100%> (ø)	:arrow_up:
R/fitMC.R	8.91% <8.91%> (ø)
R/as.alienData.R	93.75% <93.75%> (ø)
... and 6 more

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