Allow x-axis markings to show when not showing negative values
Allow drawing of positive y-axis only
Refactor markings to allow separate x and y options
Increase code clarity

- Make some key names more concise
- Add comment
- Increase size of example canvas element
Allow arbitrary functions with different colors to be passed in and drawn
Refactor setter into separate set and validate

Utilize new validate method for our graph drawing function
Add MIT license
Add ability to find a single point value on a function and plot it
Change graph drawing method to take only a single function at a time

This effectively undoes earlier work that made the method take arbitrary arguments. Upon greater reflection, it seems that taking a single function, and utilizing loops outside the object calling the object methods to pass multiple functions is a more elegant approach.
Add code/naming clarify

- Remove unused var
- Improve documentation
- Improve key name for graph scaling
Add README file