Merge pull request #170 from kevgliss/export

Adding export plugin docs

docs/developer/plugins/index.rst

@@ -230,6 +230,28 @@ The `SourcePlugin` object requires implementation of one function::
 Often times to facilitate code re-use it makes sense put source and destination plugins into one package.
 
 
+Export
+------
+
+Formats, formats and more formats. That's the current PKI landscape. See the always relevant `xkcd <https://xkcd.com/927/>`_.
+Thankfully Lemur supports the ability to output your certificates into whatever format you want. This integration comes by the way
+of Export plugins. Support is still new and evolving, the goal of these plugins is to return raw data in a new format that
+can then be used by any number of applications. Included in Lemur is the `JavaExportPlugin` which currently supports generating
+a Java Key Store (JKS) file for use in Java based applications.
+
+
+The `ExportPlugin` object requires the implementation of one function::
+
+    def export(self, body, chain, key, options, **kwargs):
+        # sys.call('openssl hokuspocus')
+        # return "extension", passphrase, raw
+
+
+.. Note::
+Support of various formats sometimes relies on external tools system calls. Always be mindful of sanitizing any input to
+these calls.
+
+
 Testing
 =======