Add custom shell completion scripts

They are based on the shell completion scripts generated by kingpin in
alecthomas/kingpin#252. Modified to complete commands after '--'.

Fixes 99designs#70

.gitignore

@@ -1,3 +1,3 @@
-aws-vault
-aws-vault-*
+/aws-vault
+/aws-vault-*
 .DS_Store

completions/bash/aws-vault

@@ -0,0 +1,17 @@
+_aws-vault_bash_autocomplete() {
+    local i cur prev opts base
+
+    for (( i=1; i < COMP_CWORD; i++ )); do
+        if [[ ${COMP_WORDS[i]} == -- ]]; then
+            _command_offset $i+1
+            return
+        fi
+    done
+
+    COMPREPLY=()
+    cur="${COMP_WORDS[COMP_CWORD]}"
+    opts=$( ${COMP_WORDS[0]} --completion-bash "${COMP_WORDS[@]:1:$COMP_CWORD}" )
+    COMPREPLY=( $(compgen -W "${opts}" -- ${cur}) )
+    return 0
+}
+complete -F _aws-vault_bash_autocomplete -o default aws-vault

completions/zsh/_aws-vault

@@ -0,0 +1,24 @@
+#compdef aws-vault
+
+_aws-vault() {
+    local i
+    for (( i=2; i < CURRENT; i++ )); do
+        if [[ ${words[i]} == -- ]]; then
+            shift $i words
+            (( CURRENT -= i ))
+            _normal
+            return
+        fi
+    done
+
+    local matches=($(${words[1]} --completion-bash "${(@)words[1,$CURRENT]}"))
+    compadd -a matches
+
+    if [[ $compstate[nmatches] -eq 0 && $words[$CURRENT] != -* ]]; then
+        _files
+    fi
+}
+
+if [[ "$(basename -- ${(%):-%x})" != "_aws-vault" ]]; then
+    compdef _aws-vault aws-vault
+fi