fix umlauts and special characters in contexts
fix umlauts and special characters in contexts

Prior to this change, umlauts and other special characters would not be allowed in contexts.

For example, the task "#TODO: contact @Müller" would be detected to include the context "M" instead of "Müller". Similarly, ""#TODO: contact @Hans_Müller" would be detected as containing "Hans" instead of "Hans_Müller".

By matching against any non-space characters - similar to the tags regex - this change fixes the above issues.
imdone/imdone-core,imdone/imdone-core