Refactor book:build task

[bagasme]

• I provide my work under the project license.
• I grant such license of my work as is required for the purposes of future print editions to Ben Straub and Scott Chacon.

Changes

This PR refactors monolithic book:build task into several smaller tasks:

1. book/contributors.txt file task: generates contributors list required to build book formats
2. book:build_html - build HTML format
3. book:build_epub - build Epub format
4. book:build_pdf - build PDF format
5. book:check - check HTML and Epub

This also add convenience tasks:

1. book:clean - clean artifacts (contributors list and books)
2. book:ci - build books with checking enforced (not ignored), targeted for CI.

Note: The CI doesn't execute book:ci, but still running book:build instead. Discussions are welcome whether the CI should switch to book:ci or not.

Context

Fixes #1595

[HonkingGoose]

What do you think of these changes?

[bagasme]

review ping

[HonkingGoose]

@ben @jnavila could you take a look at this?

[jnavila]

Thank you for proposing. These are mostly style comments.

[bagasme]

review ping

[HonkingGoose]

Suggested change

	# Check contributors list
	# This checks commit hash stored in the header of list against current HEAD
	def check_contrib
	if File.exist?('book/contributors.txt')
	current_head_hash = `git rev-parse --short HEAD`.strip
	header = `head -n 1 book/contributors.txt`.strip
	# Match regex, then coerce resulting array to string by join
	header_hash = header.scan(/[a-f0-9]{7,}/).join
	if header_hash == current_head_hash
	puts "Hash on header of contributors list (#{header_hash}) matches the current HEAD (#{current_head_hash})"
	else
	puts "Hash on header of contributors list (#{header_hash}) does not match the current HEAD (#{current_head_hash}), refreshing"
	`rm book/contributors.txt`
	# Reenable and invoke task again
	Rake::Task['book/contributors.txt'].reenable
	Rake::Task['book/contributors.txt'].invoke
	end
	end
	end
	# Check contributors list
	# This checks the commit hash stored in the header of the list against the current HEAD
	def check_contrib
	if File.exist?('book/contributors.txt')
	current_head_hash = `git rev-parse --short HEAD`.strip
	header = `head -n 1 book/contributors.txt`.strip
	# Match regex, then coerce resulting array to string by join
	header_hash = header.scan(/[a-f0-9]{7,}/).join
	if header_hash == current_head_hash
	puts "Hash on header of contributors list (#{header_hash}) matches the current HEAD (#{current_head_hash})"
	else
	puts "Hash on header of contributors list (#{header_hash}) does not match the current HEAD (#{current_head_hash}), refreshing"
	`rm book/contributors.txt`
	# Re-enable and invoke task again
	Rake::Task['book/contributors.txt'].reenable
	Rake::Task['book/contributors.txt'].invoke
	end
	end
	end

Some small comment fixes.

[jnavila]

The build is failing with syntax error.

[bagasme]

review ping

[jnavila]

It looks good to me. Thank you very much!

[shi1647ra]

#1610