_build_config
Construct the configuration file. Config file is looked for in three locations:
ENV
lib/Mojito/conf/mojito_local.conf
lib/Mojito/conf/mojito.conf
The values will be merged with the precedent order being:
ENV over
mojito_local.conf over
mojito.conf
read_config
Args: a configuration file name
Returns: a HashRef of configuration values
merge_hash
Args: ($hash_ref_dominant, $hash_ref_subordinate)
Returns: HashRef of the two merged with the dominant values
chosen when they exist otherwise the subordinate values are used.