Add roadmap notes to README

Author: PaintYourDragon

README.md

@@ -19,3 +19,13 @@ Recent Arduino IDE releases include the Library Manager for easy installation. O
 - 'Fonts' folder contains bitmap fonts for use with recent (1.1 and later) Adafruit_GFX. To use a font in your Arduino sketch, #include the corresponding .h file and pass address of GFXfont struct to setFont(). Pass NULL to revert to 'classic' fixed-space bitmap font.
 
 - 'fontconvert' folder contains a command-line tool for converting TTF fonts to Adafruit_GFX .h format.
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+---
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+### Roadmap
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+The PRIME DIRECTIVE is to maintain backward compatibility with existing Arduino sketches -- many are hosted elsewhere and don't track changes here, some are in print and can never be changed! This "little" library has grown organically over time and sometimes we paint ourselves into a design corner and just have to live with it or add ungainly workarounds.
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+Highly unlikely to merge any changes for additional or incompatible font formats (see Prime Directive above). There are already two formats and the code is quite bloaty there as it is (this also creates liabilities for tools and documentation). If you *must* have a more sophisticated font format, consider creating a fork with the features required for your project. For similar reasons, also unlikely to add any more bitmap formats, it's getting messy.
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+Please don't reformat code for the sake of reformatting code. The resulting large "visual diff" makes it impossible to untangle actual bug fixes from merely rearranged lines.