Increase test coverage

Changes in test suite:
- adding functional tests for `FuncSpec` class
- reorganizing a bit and adding new functional tests for ODE generators
- converting test for MapSystem to use with py.test

Also PR includes:
- update in Travis CI configuration to support http://coveralls.io
- new root Makefile to simplify common tasks
- build and coverage badges in README.md (needs adjusting for main repo after merging)