valid header adornemets not autocompleted

[mgaitan]

the header autocompletion trigger only recognize a very reduced subset of valid adornments characters.

{ "key": "preceding_text", "operator": "regex_contains", "operand": "^[=\\-\\*\\+]+" }

So if you have something like

A valid header
~~~<TAB> 

It wont be autocompleted.

Complete the regex operand with a complete list of valid adornemets . In python it is:

ADORNEMENTS = r"""[!\"#$%&'\\()*+,\-./:;<=>?@\[\]\^_`{|}~]"""