Move global variables into `game_constants` module
Port order will have to be some more complicated map eventually.
Add a required method to board_geometry. Hexagon_neighbors.
Tests for StandardBoard.hexagon_neighbors
Board._connect_tiles method and test.

This method takes the tiles (in order) and creates an edge between
each of them. This allows for simpler querying of neighbors.
Removed line length 120 allowance & flake8 fixes.
hexagon_utils.neighbors interface clarification.
Add vertex_synonyms to board_geometry and tests.
Revised board docs, internals, test layout.
Removed Connection class
flake8 fixes.
Merge pull request #5 from Wilduck/board-methods

Better board setup.