adding basics on ptr vs value receiver

remove bogus code in slicingmistakes

apply proper naming conventions to SentinelErr

adding an example of concurrency with error handling propagation

bump x/sync

more docs on errors

add error_wrapping learning materials

(chore) 🚀 update submodules

(chore) 🚀 update submodules

update pointer to learning-go-book submodule

update pointer to learning-go-book submodule

adding learning-go-book as a submodule reference

adding .interfaces with basic example

basics on sync.errGroup

adding a .concurrency_patterns dir

apply go fmt

adding examples of Single Responsibility Principle

adding testify dependency

SOLID & Patterns

adding json & xml modules; update all table of contents links for…

50: Regular expression examples

49 & 50: Placeholders and start on Regexp

48: boilerplate for string formatting

81: Notes and examples of using os.Exit(..)

80: Example of handling UNIX signals

80: Boilerplate for signals

79: Executing commands using syscall & exec

78: Spawning example with piping

78: Spawning processes