Refactor and introduce metarw mode

Merged logs:
- Add metarw plugin
- Add write command
- Bug fix
- Make write silent
- Split listEntry > getListFeed, saveListFeed
- Split hatena#detailEntry into small functions
- Add mode line
- Merge fix into autoload/hateblo.vim
- Split out some functions (not tested)
- Split out s:ask_update, s:check_draft, s:update_entry
- Rewrite hateblo#metarw#write
- Split s:create_entry
- Merge s:get_category_str and map(...) into s:get_category
- Introduce s:ask
- Refactor createEntry
- Small fix
- Split s:get_title_from_lines, s:ask_title
- Create hateblo#newEntry
- Bug fix
- Add 'New Entry'
- Use s:ask in deleteEntry()
- Refine s:get_title
- Rearrange functions
- Introduce s:{title,category}_prefix
- Implement s:strip_header
- The argument of getFeed is fixed
- Merge updateEntrySilent
- Bug fix
- Remove space lines
- Rename s:create_entry > s:create
- Rename s:update_entry > s:update
- Rename s:strip > s:strip_whitespace
- Rename s:add_space > s:prepend_space
- Rename s:rectify_lines > s:format_lines
- Modify s:category_str into s:get_entry_category
- Sort functions
- Rename s:save_buffer_value > s:save_entry_meta_to_buffer
- Make hateblo#saveFeed local (s:save_feed_meta_to_buffer)
- Make hateblo#getEntry local (s:get)
- Rename hateblo#{next,first}Page > hateblo#get{next,first}PageLink
- Rename hateblo#entryID > hateblo#getEntryID
- Bug fix in s:get_title (consider null string case)
- Remove argument of s:check_draft
- Fix flow diagram about entry_id
- Fix s:strip_header to allow empty first line
- Not to save with `:w`