update readme, add circuit examples dir, add vim/nvim .circuit syntax highlighter

vim-syntax/README.md

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+# circuit vim syntax
+
+## Installation in vim/nvim using plug
+Using [Plug](https://github.com/junegunn/vim-plug), add this lines into the `.vimrc`/`init.vim`:
+```
+Plug 'arnaucube/go-snark'
+Plug 'arnaucube/go-snark', {'rtp': 'vim-syntax'}
+```
+
+![screenshot-vim](https://raw.githubusercontent.com/arnaucube/go-snark/master/vim-syntax/screenshot.png "screenshot-vim")

vim-syntax/ftdetect/go-snark-circuit.vim

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+au BufRead,BufNewFile *.circuit set filetype=go-snark-circuit

vim-syntax/syntax/go-snark-circuit.vim

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+" Vim syntax file
+" Language:	go-snark-circuit
+" URL:		https://github.com/arnaucube/go-snark/blob/master/vim-syntax/syntax/go-snark-circuit.vim
+
+if !exists("main_syntax")
+  " quit when a syntax file was already loaded
+  if exists("b:current_syntax")
+    finish
+  endif
+  let main_syntax = 'go-snark-circuit'
+elseif exists("b:current_syntax") && b:current_syntax == "go-snark-circuit"
+  finish
+endif
+
+let s:cpo_save = &cpo
+set cpo&vim
+
+syn keyword goSnarkCircuitCommentTodo      TODO FIXME XXX TBD contained
+syn match   goSnarkCircuitLineComment      "\/\/.*" contains=@Spell,goSnarkCircuitCommentTodo
+syn match   goSnarkCircuitSpecialCharacter "'\\.'"
+syn match   goSnarkCircuitNumber	       "-\=\<\d\+L\=\>\|0[xX][0-9a-fA-F]\+\>"
+syn match goSnarkCircuitOpSymbols "+\|-\|\*\|:\|)\|(\|="
+syn keyword goSnarkCircuitPrivatePublic		private public
+syn keyword goSnarkCircuitOut	out
+syn keyword goSnarkCircuitEquals	equals
+syn keyword goSnarkCircuitFunction	func
+syn match goSnarkCircuitFuncCall /\<\K\k*\ze\s*(/
+syn keyword goSnarkCircuitPrivate private nextgroup=goSnarkCircuitInputName skipwhite
+syn keyword goSnarkCircuitPublic public nextgroup=goSnarkCircuitInputName skipwhite
+syn match goSnarkCircuitInputName '\i\+' contained
+syn match	goSnarkCircuitBraces	   "[{}\[\]]"
+syn match	goSnarkCircuitParens	   "[()]"
+
+syn sync fromstart
+syn sync maxlines=100
+
+" Define the default highlighting.
+" Only when an item doesn't have highlighting yet
+hi def link goSnarkCircuitLineComment		Comment
+hi def link goSnarkCircuitCommentTodo		Todo
+hi def link goSnarkCircuitSpecialCharacter	Special
+hi def link goSnarkCircuitNumber		Number
+hi def link goSnarkCircuitOpSymbols		Operator
+hi def link goSnarkCircuitFuncCall		Function
+hi def link goSnarkCircuitEquals		Identifier
+hi def link goSnarkCircuitFunction		Keyword
+hi def link goSnarkCircuitBraces		Function
+hi def link goSnarkCircuitPrivate 		Keyword
+hi def link goSnarkCircuitPublic		Keyword
+hi def link goSnarkCircuitInputName		Special
+hi def link goSnarkCircuitOut   		Special
+hi def link goSnarkCircuitPrivatePublic		Keyword
+
+let b:current_syntax = "go-snark-circuit"
+if main_syntax == 'go-snark-circuit'
+  unlet main_syntax
+endif
+let &cpo = s:cpo_save
+unlet s:cpo_save
+
+" vim: ts=8