vim: change gvim's default size
vim: always use a non-blinking block cursor in gvim
vim: don't use autoselect, gui tabs, or scrollbars in gvim
vim: remove unnecessary function and mapping; fix typo
vim: fix relative number toggle
vim: change some textwidth options

 * use 80 columns
 * use position relative to textwidth for colorcolumn
 * break long lines
vim: change wildmode; show the list right from the very first use
vim: change behavior when switching buffers

When switching between buffers, jump to the first window that contains
the specified buffer. Consider only windows from the current tab.
vim: change horizontal scroll behavior

 * move one column at a time; don't jump in the middle of the screen
 * have at least 5 columns at the left and right of the cursor
vim: upon split put window always below or right
vim: change completion behavior

 * don't scan included files
 * don't show preview window
vim: use emacs-style command-line editing keys
vim: add mappings for windows and tabs

 * split window with <leader>+| or <leader>+-
 * open a new tab with <leader>+T
 * move between windows with alt+(h,j,k,l)
 * resize window with alt+(left,down,up,right)
 * move between tabs with gh, gl or ctrl+(left,right)
vim: don't use alt key to access the gui menus
vim: use 5 columns for the line numbers

Now we can have up to 4-digit numbers
without a resize of the number column.
vim: show folds column; add a toggle mapping
vim: use terminalkeys plugin; fix vim under screen and tmux

Necessary for some keys to work properly under screen and tmux.
vim: put autocommands in autogroup and reset it on loading

Avoid duplicate autocommands.
vim: move by screen lines instead of physical lines
vim: change mapping and key code timeout