Add CircuitPython_SynthVoice library

Author: relic-se

.gitmodules

@@ -463,3 +463,6 @@
 [submodule "libraries/helpers/iperf"]
 	path = libraries/helpers/iperf
 	url = https://github.com/bablokb/circuitpython-iperf.git
+[submodule "libraries/helpers/synthvoice"]
+	path = libraries/helpers/synthvoice
+	url = https://github.com/relic-se/CircuitPython_SynthVoice.git

circuitpython_community_library_list.md

@@ -138,6 +138,7 @@ c* [CircuitPython_RotarySelect](https://github.com/FoamyGuy/CircuitPython_Rotary
 * [CircuitPython Slider](https://github.com/jposada202020/CircuitPython_slider.git) Simpleslider for Touchscreens ([PyPi](https://pypi.org/project/circuitpython-slider/)) \([Docs](https://circuitpython-slider.readthedocs.io/en/latest/))
 * [CircuitPython SoftKeyboard](https://github.com/FoamyGuy/CircuitPython_SoftKeyboard.git) Soft Keyboard for Touchscreens ([PyPi](https://pypi.org/project/circuitpython-softkeyboard/)) \([Docs](https://circuitpython-softkeyboard.readthedocs.io/en/latest/))
 * [CircuitPython Styles](https://github.com/jposada202020/CircuitPython_styles.git) Library helper to add styles to CircuitPython display functions CircuitPython widgets ([PyPi](https://pypi.org/project/circuitpython-styles)) \([Docs](https://circuitpython-styles.readthedocs.io/en/latest/))
+* [CircuitPython_SynthVoice](https://github.com/relic-se/CircuitPython_SynthVoice/) Helper library to generate complex synthio voices. \([Docs](https://circuitpython-synthvoice.readthedocs.io/en/latest/))
 * [CircuitPython_TemperatureTools](https://github.com/CedarGroveStudios/CircuitPython_TemperatureTools.git) A collection of Dew Point, Heat Index, and  temperature unit helpers \([Docs](https://github.com/CedarGroveStudios/CircuitPython_TemperatureTools/blob/main/media/pseudo_rtd_cedargrove_temperaturetools.pdf))
 * [CircuitPython_TMIDI](https://github.com/todbot/CircuitPython_TMIDI.git) Alternate CircuitPython MIDI library, inherits from Winterbloom_SmolMIDI ([PyPi](https://pypi.org/project/circuitpython-tmidi/)) \([Docs](https://circuitpython-tmidi.readthedocs.io/en/latest/))
 * [CircuitPython_TOML](https://github.com/elpekenin/circuitpython_toml.git) A subset of CPython's built-in module for working with TOML data. Useful for complex data on `settings.toml` where `os.getenv` is not enough.