Back in March, Ruby developer Gregory Brown raised the idea of receiving donations so he could work on open source Ruby projects full-time. It went well, and out of this project came Prawn, a pure Ruby PDF generation library. Not one to rest on his laurels, Gregory's now working on a book for O'Reilly called Ruby Best Practices, billed as "for programmers who want to use Ruby the way Rubyists do." The book will cover how to design "beautiful" APIs and…