SVGHMI: add support for multiline widget declaration using svg:desc.
Declaration started in inkscape:label and interupted by a '\' can be continued in the description field.
After an empty line, the rest of the description field is left for description text.
.project
.svghmithumbs
.directory
.pytest_cache
.cache
.coverage_full
syntax: regexp
^tests/.*/build$
^exemples/.*/build$
^.idea/.*
syntax: regexp
^.*\.pyc$
syntax: regexp
^.*~$
syntax: regexp
^.*\.swp$
bug_report.*\.txt
i18n/.*.new$
revision
doc/_build
doc/locale