Merge tag '0.3' into develop

Version 0.3
feat: tvd.create explicit error message
feat: work in progress
Merge tag '0.3.1' into develop

Version 0.3.1
feat: AnnotationGraph.relabel_floating_nodes()
doc: docstring ascii art for graph handling
feat: AnnotationGraph.{pre|post}_align()
work in progress
feat: Plugin.download_as_text()
feat: download_as_utf8 with character mapping
fix: download_as_text replaced by download_as_utf8
feat: track TVD version in graph
feat: track TVD plugin version in graph
feat: give to Caesar what belongs to Caesar
doc: CHANGELOG
Merge branch 'release/0.4'