added generation of a help mojo

now this gives

$ mvn com.lewisd:lint-maven-plugin:0.0.8-SNAPSHOT:help -Dgoal=check -Ddetail=true
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building Maven POM lint plugin 0.0.8-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- lint-maven-plugin:0.0.8-SNAPSHOT:help (default-cli) @ lint-maven-plugin ---
[INFO] Maven POM lint plugin 0.0.8-SNAPSHOT
  Generates a report of suspicious/inconsistent POM elements, and optionally
  fails the build if violations are found.

lint:check
  Perform checks on the POM, and fail the build if violations are found.

  Available parameters:

    configLocation
      The root spring config location.
      Required: Yes

    failOnViolation
      Fail the build when there are violations.

    htmlOutputFile
      Specifies the path and filename to save the HTML report to.

    outputReports
      Comma-separates list of output reports to generate.
      Supported reports are:
      summary (written to standard out, or file specified by summaryOutputFile)
      xml (written to file specified by xmlOutputFile)
      html (written to file specified by xmlOutputFile) (NOT YET IMPLEMENTED)

    xmlOutputFile
      Specifies the path and filename to save the XML report to.

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.281s
[INFO] Finished at: Sat Aug 24 11:34:17 CEST 2013
[INFO] Final Memory: 7M/188M
[INFO] ------------------------------------------------------------------------