Add support for external example files

[mkienow-r7]

Description

Adds support for external example files.

Motivation and Context

Increases feature parity with other recog language implementations. rapid7/recog#382 introduced this feature into the Ruby language implementation.

How Has This Been Tested?

• New unit tests
• mvn clean install -DskipITs
• mvn integration-test - this will fail until the xml/telnet_banners.xml changes are landed in rapid7/recog and available via Ruby Gems
• The com.rapid7.recog.verify.RecogVerifier tool with local fingerprints using external example files. These fingerprints included a subset from xml/ldap_searchresult.xml where the base64 example data was decoded into external example files.

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• I have updated the documentation accordingly (or changes are not required).
• I have added tests to cover my changes (or new tests are not required).
• All new and existing tests passed.