PWM Generator Enclosure

An enclosure for the basic 4 button PWM generator module. This is a re-mix of the design by fxch (https://www.thingiverse.com/thing:3215646), as I wanted access to all the pins but didn't need the USB/UART module. This design also fixes the following issues:

1) The buttons on the original simply don't work, they bottom out on the switch body before actuating the switch. They are also poorly retained in the case and fall out easily. All four buttons are now printed as a single part, making assembly easier and making it impossible for them to fall out.
2) The buttons were not all correctly centred over the switches (minor issue)
3) The cut out for the LCD screen had extremely thin (1 or 2 layer) bezels that were easy to break just removing the case from the print bed. The cut out was also not well centred on the LCD. This has a significantly deeper bezel with a nice 45 degree chamfer.
4) The slot for the PWM output pins was not correctly centred, there was not enough room to