Implement Look around

[User4martin]

-=- (+) Added full look-ahead support. Added full fixed length look-behind support.Added limited variable length look-behind support. -=- (+) Added (?modifier:pattern) support. -=- (+) Added "property AllowBraceWithoutMin" to allow {,2} instead of {0,2}. -=- (+) Added "property AllowLiteralBraceWithoutRange" to allow "{" to be matched as literal, if no range follows.

Fixes:

302

298

Part of #285

[Alexey-T]

Great work! @andgineer Please apply, Martin added tests.

[Alexey-T]

@User4martin Pls fix version to 163

  // TRegExpr.VersionMajor/Minor return values of these constants:
  REVersionMajor = 1;
  REVersionMinor = 160;

[Alexey-T]

@andgineer Lets apply?