This pull request address #26 by providing functionality to visualise e-graph using a consistent style with egglog. The main modified file is Dot.hs, which contains detailed haddock documentation.

Main usage:

• the function toDotFile' allow user to customise how analysis and e-nodes are displayed as Text
• the function toDotFile is a special default case for toDotFile' based on the Show instances

Notes for reviewer (@alt-romes):

• The last commit is only for a minimal test of the visualisation, which generates the e-graph for SimpleSym test case at the root. Feel free to exclude or modify how this test should be integrated.
• The visualisation has the same limitation with the egglog one, which is that self pointed edges (x -> e-class of x) are not pointing to the e-class boundary but a inner e-node. This is a known limitation of Graphviz pointed out in the rust implementation.
• (A slight difference with egglog) The e-class clusters are filled with grey instead of being colorful. In egglog colours are used to distinguish the different types of terms. This is not very relevant for now but could be added in the future.