Fix pandoc citation autocompletions

wiki.vim overwrites omnifunc for any buffer it sees as its own. Pandoc
uses g:pandoc#competion#Complete as its omnifunc to generate citations.

So we use deoplete to collect the citations and display them on being
invoked by `@`. When typing more, it filters the list accordingly.

Have not gotten preview window working again, nor searching of fields
other than bibkey.

nvim/.config/nvim/plugin/deoplete.vim

@@ -0,0 +1,22 @@
+" PLUGIN: DEOPLETE
+" For async completion
+" enable deoplete at startup
+let g:deoplete#enable_at_startup =1
+let g:deoplete#enable_ignore_case =1
+let g:deoplete#enable_smart_case =1
+let g:deoplete#enable_camel_case =1
+let g:deoplete#enable_refresh_always =1
+let g:deoplete#max_abbr_width =0
+let g:deoplete#max_menu_width =0
+
+call deoplete#custom#var('omni', 'input_patterns', {
+      \'pandoc': '@\w*',
+      \})
+call deoplete#custom#var('omni', 'functions', {
+      \'pandoc': 'pandoc#completion#Complete',
+      \})
+call deoplete#custom#option({
+ \ 'auto_complete_delay': 0,
+ \ 'smart_case': v:true,
+ \})
+