Introduced a solution that automatically shrinks down the prompt if the shell is low on space, fixed several bugs.

• Introduced a system for shell segment priorities, which, if space is limited, removes segments with lowest priority first. This can be controlled with the -priority flag, with decreasing priority.
• Introduced -maxwidth, specifying the maximum width (in percent) of the shell that the prompt may take up. Default is 50
• Fixed an issue where segment-cwd could read out of bounds