Fix enew handling

Closes #33.
Remove VimEnter event after execution
Optionally restore cursor position

This uses the '" mark to restore the last cursor position when opening a
file, implemented as BufReadPost autocmd.
Merge branch 'restore-cursor-position'
Bump to 1.7
Clean up VimEnter autocmd
Doc: g:startify_list_order
Fix the use of s:numfiles
Doc: add NERDTree hint to FAQ
New option: g:startify_session_detection
Refactor set_mark() and open_buffers()
Refactor open_buffers() pt2
Change into dir also for bookmarked dirs

References #32.
Remove useless concatenation
New option: g:startify_session_autoload
User some helper variables
Doc: add another FAQ because of NERDTree
Fix indexing for certain list orders

References #32.
Merge branch 'improve-sessions'

References #32.
New option: g:startify_session_persistence

Whenever you load/save a session, v:this_session is set automatically.
If this option is enabled and v:this_session exists, the session file
will be updated before exiting Vim.

References #32.