Added ability to use custom assembly containing embedded R# annotations

[jpeirson]

Simply modify the FodyWeavers.xml file with a couple of attributes to enable this behavior, e.g.:

<Weavers>
  <JetBrainsAnnotations assembly="MyInternalResharperAnnotations" remove="true"/>
</Weavers>

See also updated section in README.md.

[jpeirson]

Fixed issue with using wrong Config element, for modifying own assembly.