Add a mechanism for building a cache of "system parameters"

- Add a system_parameters module to eryntools that implements some basic types and can write a cache to a file.
- Add a system-parameters Python script that builds the cache.
- Add init_system_parameters to zsh that exports an environment variable that points to the parameters file
- Add an eryn.system-parameters.plist LaunchAgent file for running the script at regular intervals

zsh/func/init_system_parameters

@@ -0,0 +1,15 @@
+#!/usr/bin/env zsh
+# Eryn Wells <eryn@erynwells.me>
+
+function init_system_parameters
+{
+    local PARAMETERS_FILE="$HOME/.config/eryn/system_parameters"
+
+    if [[ ! -e "$PARAMETERS_FILE" ]]; then
+        return
+    fi
+
+    export SYSTEM_PARAMETERS_FILE="$PARAMETERS_FILE"
+}
+
+init_system_parameters "$@"