Support the ability to parse sections of a configuration file

1. Exposing another method for parsing configuration files.
This method takes as an optional parameter a group. This group specifies which section of the configuration file pertains to the options being parsed.

e.g.
DisconverViaDns: true
CustomSection:
    Key: x
    AnotherKey: y

This "CustomSection" can then be parsed by specifying the section in the configuration 
   EventStoreOptions<CustomOptions>(contentsOfConfig, "CustomSection")