Support more anchors (meta-issue)

[kddnewton]

We already support some anchors for regex, but we should support all of them. They are listed below:

• ^ - Matches beginning of line
• $ - Matches end of line
• \A - Matches beginning of string.
• \Z - Matches end of string. If string ends with a newline, it matches just before newline
• \z - Matches end of string
• \G - Matches first matching position
• \b - Matches word boundaries when outside brackets; backspace (0x08) when inside brackets
• \B - Matches non-word boundaries