Merge pull request #1 from vincentbernat/fix/flexible-certs

security: be more liberal in what kind of PEM files are accepted
nitpicks & KNF
pre-compile all namespaces
security: fallback to default key if a specific host key is not found

This is convenient for tests since we can provide example configuration
that will work without modifications.
doc: provide a minimal configuration

A configuration file that should work without any external environment
is provided. We also provide the matching configuration file for the
agent.