Add toml struct tags
https://github.com/burntsushi/toml
is used to marshal a toml struct to
the config.Global
struct. This marshaling was done automatically by
the name of the field. This can lead to expected breaking changes for
example we do a rename of the struct field and we end up breaking
existing configuration because of the rename. Struct tags ensure that we
don't do any breaking change by any kind of refactoring and also make it
clear/explicit that we are marshaling this struct into toml
closes #11 (closed)