add char, outputs SymPy "srepr" representation

Partial fix for #91.
sym: improve symfun matching and creation from raw srepr

Use a regex for more accurately determining user wants symfun.
Fixes #94.  This allows srepr input: fixes #91.
Merge pull request #93 from cbm755/fix_91

add char method, sym ctor takes srepr, improve symfun false negatives
Merge remote-tracking branch 'origin/master' into depr2

Conflicts:
	NEWS
display: reduce left margin by one space

Consider "display([-1 1])" if you need *justification* ;-)