DOC: update scikit-xray -> scikit-beam
DOC: update scikit-xray -> scikit-beam

Update to reflect the org name change from scikit-xray to scikit-beam
and the repo name change from scikit-xray to scikit-beam. Note that
there is still a major overhaul needed to rename the skxray python
package to skbeam

ericdill/scikit-xray,tacaswell/scikit-xray,tacaswell/scikit-beam,yugangzhang/scikit-beam,Nikea/scikit-xray,licode/scikit-xray,scikit-xray/scikit-xray,danielballan/scikit-xray,CJ-Wright/scikit-beam,yugangzhang/scikit-beam,Nikea/scikit-xray,tacaswell/scikit-xray,licode/scikit-xray,licode/scikit-beam,yugangzhang/scikit-beam,scikit-xray/scikit-xray,danielballan/scikit-xray,CJ-Wright/scikit-beam,licode/scikit-beam,tacaswell/scikit-beam,scikit-xray/scikit-xray,Nikea/scikit-xray,danielballan/scikit-xray,licode/scikit-beam,ericdill/scikit-xray,CJ-Wright/scikit-beam,tacaswell/scikit-xray,ericdill/scikit-xray,tacaswell/scikit-beam,licode/scikit-xray