WIP: add map type
WIP: Update from Dense_HODLR

Amir Writes:  Just wanted to let you know that ive
added the fast determinant estimation as per
Fast Direct Methods for Gaussian Processes and the Analysis of NASA Kepler Mission Data
Also there is an additional solve method called recSM_Solve
which uses the Sherman Morrison formula.
Merge branch 'master' of github.com:stnava/RHODLR
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