When loading a config, if some options are missing, use default values
for them instead. So that it is not necessary to copy luacov.defaults completely, only options with non-default values have to be set.
Repushed a fixed version which does not expose set_config function and keeps non-standard options which other luacov related tools may use (e.g. luacov-coveralls).
When loading a config, if some options are missing, use default values for them instead. So that it is not necessary to copy luacov.defaults completely, only options with non-default values have to be set.