presence: New parser

Adopt an easy on the tongue acronym similar to other projects.
Add a robust parser with support for sensors and policies.
  Sensors: gpio, tach
  Policies: fallback
Add an example yaml file.

Change-Id: I9158a0ce2a08ef6b7bb3f5d659ea0e0433af5b96
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/presence/templates/gpio.mako.hpp b/presence/templates/gpio.mako.hpp
new file mode 100644
index 0000000..fb1f46f
--- /dev/null
+++ b/presence/templates/gpio.mako.hpp
@@ -0,0 +1,2 @@
+std::make_unique<PolicyAccess<Gpio, ConfigPolicy>>(
+${indent(1)}${g.policy}, "${g.physpath}"s, ${g.key})\