Support for Marginalia multidoc generation

Marginalia can generate documentation for each namespace as a separate file. This commit adds a configuration option to the "marginalia" map to support this feature.

Usage:

  <plugin>
    <groupId>com.theoryinpractise</groupId>
    <artifactId>clojure-maven-plugin</artifactId>
    <version>1.3.14-SNAPSHOT</version>
    <configuration>
      <marginalia>
        <multi>true</multi>
      </marginalia>
    </configuration>
  </plugin>
Merge tag '1.3.14' into develop

Rel

* tag '1.3.14':
  [maven-release-plugin] prepare for next development iteration
  [maven-release-plugin] prepare release clojure-maven-plugin-1.3.14
fix typo that prevented clojure:nrepl & clojure:swank from working
Merge pull request #67 from alexott/develop

fix typo that prevented clojure:nrepl & clojure:swank from working
Merge pull request #66 from sthuebner/multidoc

Support for Marginalia multidoc generation
[maven-release-plugin] prepare release clojure-maven-plugin-1.3.15
[maven-release-plugin] prepare for next development iteration
Merge branch 'release/1.3.15'

* release/1.3.15:
  [maven-release-plugin] prepare for next development iteration
  [maven-release-plugin] prepare release clojure-maven-plugin-1.3.15
  fix typo that prevented clojure:nrepl & clojure:swank from working
  Support for Marginalia multidoc generation