Servlet initialization fix

Fixes the following:

1. Read the highest numerical index of data subfolders to determine the servlet count and then creating servlets in a simple range loop based on that count.

2. Add `defaultServletCount` so that tests can run consistently across machines. The results of the histogram test were dependent on the number of servlets.

3. Removes fancy bit twiddling code (`bit.go`).

4. Adds simple masking code to replace bit twiddling code (`hash.go`). Sky splits the 64-bit FNV1a hash of the object id into a 32-bit hash for the servlets to shard off of and a 32-bit hash for the nodes to shard off of.

/cc: @boourns @snormore @orenmazor
Fixes #112.