Generate pursuit data from a list of libraries

first steps; still quite incomplete

TODO:
* don't put git output and data onto the same output stream (currently
  both go to stdout)
* handle the case where 'tmp' already exists
* include Prelude in generated data
Add Prelude
Don't die if the directory exists
Don't mix up git output with json data
add a few more libraries
include package name in search results
Add libraries.json as command line argument
Remove (now redundant) Libraries.hs
get libraries json data from stdin
checkout the most recent tagged version

... of each library before generating the data.
Add package version to output data
Fail when no suitable tags found
add 'getting your lib included' instructions
minor language style edits
language edit
Separate libraries from entries in generated data
fix a little bug
Remove unused code (there's only a tiny bit)
update frontend to work with new data.json structure
Merge pull request #17 from hdgarrood/new-libraries-2

Generate pursuit data from a list of libraries