feat(shell): improve zsh completion system (#525)

this pr adds the possibility of starting television from a different
directory and it gives the option of complete a partial match. For
example

```fish
cd ~/.config/<ctrl-t>    # opens television at '~/.config/' with an empty search bar
cd ~/.config/fi<ctrl-t>    # opens television at '~/.config/' with 'fi' in the search bar
```

solves (for zsh shell)
https://github.com/alexpasmantier/television/issues/438

television/utils/shell/completion.zsh

@@ -1,3 +1,6 @@
+# credits to the junegunn/fzf project
+# https://github.com/junegunn/fzf/blob/d18c0bf6948b4707684fe77631aff26a17cbc4fa/shell/completion.zsh
+
 _disable_bracketed_paste() {
     # Check if bracketed paste is defined, for compatibility with older versions
     if [[ -n $zle_bracketed_paste ]]; then
@@ -12,36 +15,70 @@ _enable_bracketed_paste() {
     fi
 }
 
-_tv_smart_autocomplete() {
-    emulate -L zsh
-    zle -I
+__tv_path_completion() {
+  local base lbuf suffix tail dir leftover matches
+  base=$1
+  lbuf=$2
+  suffix=""
+  tail=" "
 
-    _disable_bracketed_paste
-
-    # prefix (lhs of cursor)
-    local current_prompt
-    current_prompt=$LBUFFER
-
-    local output
-    output=$(tv --autocomplete-prompt "$current_prompt" $* | tr '\n' ' ')
-
-    if [[ -n $output ]]; then
-        # suffix (rhs of cursor)
-        local rhs=$RBUFFER
-        # add a space if the prompt does not end with one
-        [[ "${current_prompt}" != *" " ]] && current_prompt="${current_prompt} "
-
-        LBUFFER=$current_prompt$output
-        CURSOR=${#LBUFFER}
-        RBUFFER=$rhs
-
-        zle reset-prompt
-        # uncomment this to automatically accept the line
-        # (i.e. run the command without having to press enter twice)
-        # zle accept-line
+  eval "base=$base" 2> /dev/null || return
+  [[ $base = *"/"* ]] && dir="$base"
+  while [ 1 ]; do
+    if [[ -z "$dir" || -d ${dir} ]]; then
+      leftover=${base/#"$dir"}
+      leftover=${leftover/#\/}
+      [ -z "$dir" ] && dir='.'
+      [ "$dir" != "/" ] && dir="${dir/%\//}"
+      matches=$(
+        shift
+        tv "$dir" --autocomplete-prompt "$lbuf" --input "$leftover" < /dev/tty | while read -r item; do
+          item="${item%$suffix}$suffix"
+          dirP="$dir/"
+          [[ $dirP = "./" ]] && dirP=""
+          echo -n -E "$dirP${(q)item} "
+        done
+      )
+      matches=${matches% }
+      if [ -n "$matches" ]; then
+        LBUFFER="$lbuf$matches$tail"
+      fi
+      zle reset-prompt
+      break
     fi
+    dir=$(dirname "$dir")
+    dir=${dir%/}/
+  done
+}
 
-    _enable_bracketed_paste
+_tv_smart_autocomplete() {
+  _disable_bracketed_paste
+
+  local tokens prefix trigger lbuf
+  setopt localoptions noshwordsplit noksh_arrays noposixbuiltins
+
+  # http://zsh.sourceforge.net/FAQ/zshfaq03.html
+  # http://zsh.sourceforge.net/Doc/Release/Expansion.html#Parameter-Expansion-Flags
+  tokens=(${(z)LBUFFER})
+  if [ ${#tokens} -lt 1 ]; then
+    zle ${fzf_default_completion:-expand-or-complete}
+    return
+  fi
+
+  [[ ${LBUFFER[-1]} == ' ' ]] && tokens+=("")
+
+  if [[ ${LBUFFER} = *"${tokens[-2]-}${tokens[-1]}" ]]; then
+    tokens[-2]="${tokens[-2]-}${tokens[-1]}"
+    tokens=(${tokens[0,-2]})
+  fi
+
+  lbuf=$LBUFFER
+  prefix=${tokens[-1]}
+  [ -n "${tokens[-1]}" ] && lbuf=${lbuf:0:-${#tokens[-1]}}
+
+  __tv_path_completion "$prefix" "$lbuf"
+
+  _enable_bracketed_paste
 }
 
 _tv_shell_history() {