Fix the naming of the compression library, it's libXXX, the extension
configuration argument depends on where WiredTiger is installed, not
where the compression library is installed.

Don't try and specify the directory from which configure is being run.

List snappy first, bzip2 is a less likely choice.

Remove mention of the test suite to confirm compression is working.
Add zlib documentation.
Use the macro to convert NS, no need to calculate ns then convert,
just calculate us.