hrc/sh.hrc

1. more words as a label of heredocs: 
The actual EO\w+ is extremely restricted regexp to cover any kind of heredoc labels. More frequently they use any set of symbols corresponding this [\w-]+ regexp. There is no reason to restrict heredocs by using EO\w+ only. 

2. $(Process Substitution), $((Arithmetic Expansion)): 
Support of nowaday syntax for arithmetic expansions. Better highlighting of process substitution.