[nvim] Add function to show all keymappings

Use :ShowMaps to display all currently mapped things for vim. Will not
include things like `i`, but actual mappings.

.config/nvim/init.vim

@@ -358,6 +358,26 @@ call matchadd('ColorColumn', '\%81v', 100)
 " KEYBINDINGS {{{
 " ================================================================================
 "
+" Show all mapped keys in a list - from https://stackoverflow.com/questions/13990136/display-a-ordered-vim-keyboard-mapping
+function! s:ShowMaps()
+  let old_reg = getreg("a")          " save the current content of register a
+  let old_reg_type = getregtype("a") " save the type of the register as well
+try
+  redir @a                           " redirect output to register a
+  " Get the list of all key mappings silently, satisfy "Press ENTER to continue"
+  silent map | call feedkeys("\<CR>")
+  redir END                          " end output redirection
+  vnew                               " new buffer in vertical window
+  put a                              " put content of register
+  " Sort on 4th character column which is the key(s)
+  %!sort -k1.4,1.4
+finally                              " Execute even if exception is raised
+  call setreg("a", old_reg, old_reg_type) " restore register a
+endtry
+endfunction
+" use :ShowMaps to call the function
+com! ShowMaps call s:ShowMaps()      " Enable :ShowMaps to call the function
+
 " set our leader key to space since with hjkl, space is largely useless
 let mapleader = "\<Space>"
 " maps the leader for buffer local mappings (e.g. vim-waikiki for files under