QOL fixed and hopefully fixed issue with google reader and epub

Fix for epub rejected by Google Play Books, EPUBCheck (#500)

* Issue: Automate the gofmt in markdown files using gofmtmd during build
Issue Link: https://github.com/quii/learn-go-with-tests/issues/353
Modifications:
* Modified the build script to download and run the gofmtmd tool on the markdown files
* Ran the script locally and fixed the issues reported by gofmtmd tool

Note: Intro to generics md file contains some syntax related to generics which is not recognised by the tool. So some valid
code fences are not marked as go

* Issue: Errors regarding epubcheck
Issue Link: https://github.com/quii/learn-go-with-tests/issues/420
Solution:
* Corrected the SVG syntax by omitting the  version tag and dtd info
* Minorr markup corrections in md files

Test Case:
* Ran build books script locally and is able to view the generated epub file
* Added newly created epub file to Google Play books and is able to read the book

Improvements to reading files and maths chapters

12.2.0

fix imports

New chapter: Reading files

This release adds a new chapter: "Reading files", which covers using some of the new file abstractions added in Go 1.16. It also includes various improvements contributed by the community, thank you very much community!

New chapter: Reading files and other improvements

This release adds a new chapter: "Reading files", which covers using some of the new file abstractions added in Go 1.16. It also includes various improvements contributed by the community, thank you very much community!

Add go mod instructions into hello chapter

11.2.2

Update hello-world.md

Bug fix, add iteration chapter to epub

11.2.1

add missing chapter to ebook, fixing #427

Generics chapter

11.2.0

mistake in example code

Fix bug with epub: Include newer chapters

I forgot to add the newer chapters when generating the epub, oopsie

c2caa58

Minor editorial fixes

Update anti-patterns.md

Re-arranging things after some feedback

Remove some $GOPATH things from hello world

Plus some typos and grammar fixes