Plantuml-markdown

Fix

* Fixed yaml rendering with remote server (fixes 72) [Michele Tessaro]

* Removed unused `plantuml` import. [Michele Tessaro]

* Doc: fix typos. [Kian-Meng Ang]

Fix

* Removed unused `plantuml` import. [Michele Tessaro]

Changes

* Regenerated the `CHANGELOG.md` [Michele Tessaro]

* Removed dependency from plantuml package (refs 70) [Michele Tessaro]

The dependency from the `plantuml` package has been completely removed
and the only small used method was imported in the sources.

Fix

* Fixed typos in `CHANGELOG.md` [Michele Tessaro]

* Fixed external inclusions (fixes 71) [Michele Tessaro]

Added parsing of `!define` PlantUML directives to be able to include
external files when the base URL is define by a variable.
See [AWS icons Hello World](https://github.com/awslabs/aws-icons-for-plantuml#hello-world)
for an example.

New

* Added support for themes (implements 50) [Bharat Rajagopalan]

* Supported image maps from plantuml server. [Michele Tessaro]

Now png image maps are used even if the rendering is done by a remote
plantuml server.

Changes

* Various README updates. [Bharat Rajagopalan]

* Added in the README an explanation of the priority config (refs 66) [Michele Tessaro]

* Remove md_globals kwarg. [Matt Riedemann]

Markdown 3.4 dropped support for the md_globals
kwarg:

https://github.com/Python-Markdown/markdown/blob/master/docs/change_log/release-3.4.md#previously-deprecated-objects-have-been-removed

Closes 67

* Updated notes on running tests. [Michele Tessaro]

Fix

* Fixed tests. [Michele Tessaro]

Changes

* Fixed code indentation in README.md. [Michele Tessaro]

Fix

* Fixed running on Windows (fixes 63) [Michele Tessaro]

Fixed the condition for the detection of image maps: when there are no
image maps, in Linux the output is `\n` while on Windows it is `\r\n`,
so in Windows image maps were detected even if not present.

Fix

* Fixed error with external plantuml server (fixes 61) [Michele Tessaro]

When using an external PlantUML server to render diagrams, if a diagram
has syntax errors and the remote server returns an error code (HTTP >=
400), and exception was thrown immediatly stopping markdown parsing.
Now the error is intercepted and logged, and markdown can continue its
work.