fix: update GitHub URLs from master to main branch

- Replace tree/master with tree/main in all documentation and code comments
- Fix issues/168 -> pull/168 reference (issue was converted to PR)

docs/contributor/DOCUMENTATION_GUIDELINES.md

@@ -290,7 +290,7 @@ Optionally, in order to demonstrate the relation between the two, you can start
 ```
 //! > Made with *Bizinikiwi*, for *Pezkuwi*.
 //!
-//! [![github]](https://github.com/pezkuwichain/pezkuwi-sdk/tree/master/bizinikiwi/pezframe/fast-unstake) -
+//! [![github]](https://github.com/pezkuwichain/pezkuwi-sdk/tree/main/bizinikiwi/pezframe/fast-unstake) -
 //! [![pezkuwi]](https://pezkuwichain.io)
 //!
 //! [pezkuwi]: https://img.shields.io/badge/polkadot-E6007A?style=for-the-badge&logo=polkadot&logoColor=white

docs/sdk/src/guides/async_backing_guide.rs

@@ -9,7 +9,7 @@
 //!
 //! > If starting a new teyrchain project, please use an async backing compatible template such as
 //! > the
-//! > [teyrchain template](https://github.com/pezkuwichain/pezkuwi-sdk/tree/master/templates/teyrchain).
+//! > [teyrchain template](https://github.com/pezkuwichain/pezkuwi-sdk/tree/main/templates/teyrchain).
 //! The rollout process for Async Backing has three phases. Phases 1 and 2 below put new
 //! infrastructure in place. Then we can simply turn on async backing in phase 3.
 //!

docs/sdk/src/reference_docs/frame_offchain_workers.rs

@@ -111,6 +111,6 @@
 //!
 //! - <https://forum.polkadot.network/t/offchain-workers-design-assumptions-vulnerabilities/2548>
 //! - <https://exchange.pezkuwichain.app/questions/11058/how-can-i-create-ocw-that-wont-activates-every-block-but-will-activates-only-w/11060#11060>
-//! - [Offchain worker example](https://github.com/pezkuwichain/pezkuwi-sdk/tree/master/bizinikiwi/pezframe/examples/offchain-worker)
+//! - [Offchain worker example](https://github.com/pezkuwichain/pezkuwi-sdk/tree/main/bizinikiwi/pezframe/examples/offchain-worker)
 //!
 //! [`frame`]: crate::pezkuwi_sdk::frame_runtime