README modified

add '$' descriptor.
README renamed by README.md
Merge branch 'master' of https://github.com/xunzhang/Threp

Conflicts:
	README.md
README.md modified!!
awful README.md format!
Merge branch 'independent'
update remap_entry in show.py
Cache optimization of traverse in search/kdtree.py, speed up 1 min in case bilinear ll1->ll2.5.
for checkout branch update
for merge new version of Threp.
sbilinear.py and sbilinear_idw.py added and tested.