new file:   page.js
synchronize the async call of downloading chapters
minor fix
automatically detect and use the 'http_proxt` env var
bit of refactoring
minor fix
clean up
fix fetching rules for [cover url] and [author]
add concurrent fetching of chapters
new feature: package as a single epub
fix typo
add help message
include cover image
add cover page to manifest
fix jsdoc comment
[dependency] import new dependency: troll-opt to ease option parsing
[refactor]: split the page parsing process into a site-specific module
[refactor]: adopt a more OO-style method to represent index data structure.
[runtime]: new indexer for read.qidian.com
[feature]: index debugPrinter utlize colors  when stdout is connected to tty devices