Add age plugin support

See https://github.com/str4d/rage/tree/main/age-plugin.

Example usage:

	RAGE_DIR=$PWD/../Rust/rage
	(cd $RAGE_DIR; cargo build --all)
	export PATH=$PATH:$RAGE_DIR/target/debug

	age-plugin-trezor -i "John Doe" | tee trezor.id
	R=$(grep recipient trezor.id | cut -f 3 -d ' ')

	date | tee msg.txt
	rage -er $R < msg.txt > enc.txt
	rage -di trezor.id < enc.txt

setup.py

@@ -16,6 +16,8 @@ setup(
         'libagent.ssh',
     ],
     install_requires=[
+        'bech32>=1.2.0',
+        'cryptography>=3.4.6',
         'docutils>=0.14',
         'python-daemon>=2.3.0',
         'wheel>=0.32.3',