add some relevant links and other minor tweaks
Fix variable name typos in doc example
Merge pull request #27 from waldyrious/patch-1

add some relevant links and other minor tweaks
Merge pull request #28 from garborg/patch-1

Fix variable name typos in doc example
Merge pull request #26 from garborg/tests

Update test scaffolding
Interpolate when highways exit and reenter map boundaries

Cropping was leaving deleting the nodes, but leaving their keys in
highway node lists, which was breaking anything that needed
`node[highway.node[x]]`.

Tests files were also isolated in modules as the added tests behaved
differently when the file was run in isolation, and other existing
test files couldn't be run in isolation.