Replace regex in `Str::placeholders` (#37)

[Spidlace]

Related to #37

Fix issue

[bobdenotter]

Hi, @Spidlace,

If we merge this in, as-is, won't it break the behaviour that we currently use in things like title_format: "{name} - {id}" ?

[Spidlace]

Hi @bobdenotter

Sorry I didn't seen your answer I push new commit :

• I add optional bracket in regexp
• I put char in lowercase by default

And I can confirm, everythings works well with boltform (replyto_name and email) and with bolt core (when we create new page, or select fields for example)