refactor Tree and Op

CST => Tree
(now all parses uses Tree)

Tree.tmap
Op.regex

fixed doctests
`parse_token`
match "token regexes" to keep 0-space operators from wrongly parsing them (e.g. urls have "/" which is obviously not division)

`parse.body`
prefix head if operator

e.g. strings that match the "word" regex
5-HT
NT-3
Na+
1..10
__str__
(not 1.2+3.4)