update src folder links

[Arhell]

Q	A
Is bugfix?	✔️/❌
New feature?	✔️/❌
Breaks BC?	✔️/❌
Fixed issues	resolve #135

[what-the-diff]

PR Summary

• Updated PDO Documentation Link in Connection Class
  The link referring to the PDO (PHP Data Objects) documentation in the Connection class has been updated. This ensures users have access to the most current and relevant information when working with this class.

• Revised SphinxQL Documentation Link in MatchBuilder Class
  The link to the SphinxQL documentation in the MatchBuilder class has been adjusted. This update aims to refer developers to the most appropriate resources, enhancing accuracy and comprehension when using the MatchBuilder class.

• Modified SphinxQL Documentation Link in MatchExpression Class
  The link pointing to the SphinxQL documentation in the MatchExpression class has been changed. This alteration directs developers to the correct, up-to-date resources, thereby improving the understanding of the MatchExpression class functionalities.

• Refreshed PDO Documentation Links in Schema Class
  Changes have been made to the links referring to the PDO documentation within the Schema class. This serves as a provision for the right and updated references to the users, improving their knowledge of the Schema class operations.