Fixes issue with printing strings containing colons/decimals

Fix setColonOnOff() and setDecimalOnOff() not actually turning off
Fix write() with long inputs causing overlapping text

Fix MegaAVR boards (see #18)

Fix compiler warnings

• Fix flickering discussed in #16

• README formatting and links updated.
• Fix comments about setBrightness(0). It actually results in 1/16 brightness, not 0.

Switched up the order of the examples and updated the Arduino library manager link on each example.

• Cleaned up repo, source files, and examples of unnecessary files and left over comments and debug code
• Wrote test examples to test new hardware (4_displays.ino and turn_on_all_segs.ino). Made “Advanced” folder to hold them.
• @astroforge disableSystemClock() fix
• Added leading zeros to segment list
• Changed display labeling and indexing (left, leftCenter, rightCenter, right) to one, two, three, four because position naming breaks down if less than four displays are attached to bus
• Moved DefineChar example to “User Submitted” folder
• @lewispg228 ’s suggestions:
• 1. Comment that setBlinkRate() accepts floats

2. Comment on what you expect to happen in the Unkown Char example
3. MultiDisplay example - Comment on which display is which. How does the string print?
4. Start debug messages with example number and what it does
5. Break displayOptions example into two (one for brightness, one for blinking)
6. Name each example “Example_01_name”
7. Scrolling example should show how to use shiftRight() function as well

Made PROGMEM directive conditional so that library can support other processors