Add support for custom books

[wisarmy]

Specify a book file (such as TXT) , by paragraph typing test

[wisarmy]

I want to add this feature, can you give me a code design idea?

[benliepert]

I would look at how word lists are used currently. Conceptually, a custom book is sort of like a word list with randomization in terms of which group of words you're typing (a random starting point in the book) as opposed to randomly picking words to form the group. But the test shouldn't care where it got its words from, so maybe design an interface to wrap book + wordlist functionality

[wisarmy]

main...wisarmy:toipe:feature-book
The issue purpose is to test meaningful sentences in books, not random words.
I submitted an immature implementation, still missing the status of the position in the book

[benliepert]

Nice! looks good. I have a couple suggestions when you create a PR