Image filename but no path? Use document path

[thorhop]

When embedding a local image in a document one should be able to specify just the filename of the image without the need to specify path (including "./"). When specifiying a file without path Uncolored interprets that as this absolute path on my (Windows) machine:

file:///C:/Users/<user>/AppData/Local/Programs/Uncolored/0.10.2/resources/app/views/<filename>

Specifying only the filename without a path works on several other visual markdown editors.