v0.5.0 Trailing tail

[Documentation]

• README.md - Add custom method example https://github.com/fulldump/golax#support-for-google-custom-methods
• Add implementation decision # 4 https://github.com/fulldump/golax/blob/master/doc/developer.md#decision-4-custom-methods

[Routing]

• Add Google custom methods

[Others]

• Optimize routing order
• Cache some node path operations