Starts work on https as well as some moving about

I now start the listener in the main.c file rather than proxy given that
I didn't feel proxy was the right place if a normal (non-proxied)
request came in. webserver.{c,h} and proxy.{c,h} had some changes
relating to this.

The config changed slightly - we now create a folder in ~/.config/
called yaip. This is where certificates and so on will be stored along
with the user configuration

I created a helper function to get files inside this directory (it
changes based on xdg_config_home) and updated relevant tests.

In ssl.{c,h} I have started work. If they don't exist, the tool now
creates and stores a key and certificate for the CA that this tool will
need to pretend to be. I still need to write tests for this.

docs/certificate-authority.md

@@ -0,0 +1,6 @@
+# Certificate Authority
+
+At some point, it would be nice if yaip does this automatically, but for now,
+you need to create a certificate authority for yaip to sign requests with.
+
+;