www/hackernews-tui: update to 0.7.0

Brief description of application changes:

integrate Official HN APIs:
-#36: use the official APIs to display the Story View - Front Page similarly to
HN front-page.
-#37: remove StoryPooling feature and replace it with LazyLoadingComments
feature which lazily loads comments on demand.
-#39: allow all configuration options to be optional. Previously, user needs to
create the config file based the example config. Now, if an option is not
specified, a default value will be used instead (for more information/
documentation, refer to the example config file).

Brief description of codebase changes:
-Refactor the repo into 3 separate crates: hackernews_tui for main binary crate,
config_parser (lib) and config_parser_derive (proc-macro) for the libraries to
parse configuration options from the config file.
-#38: reduce the .clone() usage, move the application's hn_client::HNClient to
global state.
-small refactoring and documentation improvements

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