Add tests

[IMP1]

Add more tests to test the more intricate stuff I'm doing now.

• Test for a rule rule r1 [ 1, 2 | 1->2, 1->2 ] => [] against graph [ 1, 2 | 1->2 ]. Should this match? Make a test for it either way.
• Tests with variables just in edge labels.
• Tests for adding nodes.
• Tests for adding edges.
• Tests for changing an edge's label.
• Tests for changing an node's label.
• Tests for other features examples/split_string.blsm use.
• Tests for rational literals
• Tests for converting between rationals / reals / ints