Plantuml-markdown

Fix

* Correctly handle multiple search_dirs in PlantUMLIncluder. [Daum Alexander (DCL ATV SC D RAD CSFW FW)]

Fix

* Handled MkDocs path directives in configurations (fixes 103) [Michele Tessaro]

Fix

* Fixed source search in `base_dir` paths (fixes 102) [Michele Tessaro]

Changes

* Added a warning on `plantuml` script output (see end of 63) [Michele Tessaro]

Fix

* Fixed plantuml config file path with local rendering (fixes 101) [Michele Tessaro]

Fix

* Fixed inclusion from `mkdocs-multirepo-plugin` (refs 100) [Michele Tessaro]

Expanded the `base_dir` configuration to handle a list of paths where to
search for files to include.

New

* Added JsonSchema file for MkDocs options validation (refs 98) [Michele Tessaro]

Added a JsonSchema file which may be used with schemas in
[MkDocs-Material](https://squidfunk.github.io/mkdocs-material/) to
validate the `mkdocs.yml` configuration file.

Fix

* Fixed namespace inserted in inline svg. [Michele Tessaro]

* Fixed wrong option name in documentation (fixes 99) [Michele Tessaro]