Added FixMath to repositories.txt

[tomcombriat]

Added FixMath to repositories.txt, for acceptance in the Arduino library manager.

FixMath, a fixed point arithmetic library targeted for Arduino and cie boards.

This provides an alternative to float and double types, while using integer type under the hood which provides a performance gain for microcontrollers lacking a floating point unit.

Promotion of the internal types is processed internally and at compile time. Using standard operations between FixMath types ensures that precision is kept and overflows are avoided. FixMath tries to be conservative and do not promote types when not needed.

[github-actions]

Your submission has now been accepted! Thanks for your contribution to the Arduino Library Manager index.

The library(s) will be available for installation via Library Manager within a day's time.

You can check the logs from the Library Manager indexer for your library(s) here:
http://downloads.arduino.cc/libraries/logs/github.com/tomcombriat/FixMath/