Add ability to filter by species model, with tests
Use separate SELECT statements for querying plots versus trees

The LEFT JOINs prevent using species.id in the WHERE clause, so a normal
JOIN needs to be used instead.
Fix filterStringToWhere tests
Update README.md
Merge pull request #7 from maurizi/topic/filterSpecies

Add ability to filter by species model, with tests
Add tests for filterStringToSelect.js
Add slightly more complicated test for filterStringToSelect.js
Add docco docs for JS files
Merge pull request #12 from maurizi/topic/filterSpecies

Improvements to tiler.js
Add 'make docs' command to make file
Merge pull request #13 from steventlamb/topic/update_documentation

Add make task to build docs; update checked-in docs
Update documentation link in README.md

The file linked in the README was renamed
Filter by instance id for plots and boundaries

Both plot and boundary tiles require an instance to render the proper
subset of their respective elements. However, the method for generating
the SQL requires two different approaches.

Since we're only using one route we can just switch on the table name.
Merge pull request #14 from azavea/topic/filter-by-instance-id

Filter by instance id for plots and boundaries