Some cosmetic restructuring of readme.md, re #22.
Some cosmetic restructuring of readme.md, re #22.

Added shilds/badges for npm download and node version. (Node version is
currently N/A because it is not specified in package.json.)

Current high-level grouping in readme is: Documentation, Philosophy, and Other Feature Notes. Otherwise content is unchanged.

ryancole/hdf5.node,HDF-NI/hdf5.node,HDF-NI/hdf5.node,ryancole/hdf5.node,HDF-NI/hdf5.node,ryancole/hdf5.node