Improve parsing of key-value pairs; don't use strtok

[koekeishiya]

Pulled from #174

@dominiklohmann I feel like I'm doing something horribly wrong, because my action works when executed from a file but not when inline (re: confusion in #177 / from #167). Maybe you know what's up here.

yabai -m signal --add event=application_launched label=test action="yabai -m query --windows | jq -r '.[] | select(.pid | tostring == env.YABAI_PROCESS_ID)'"
# fails with this is on stdout
# sh: -c: line 0: unexpected EOF while looking for matching `''
# sh: -c: line 1: syntax error: unexpected end of file

# this works
export YABAI_PROCESS_ID=19210 && yabai -m query --windows | jq -r '.[] | select(.pid | tostring == env.YABAI_PROCESS_ID)'

# this works as well
/usr/bin/env YABAI_PROCESS_ID=19210 sh -c "yabai -m query --windows | jq -r '.[] | select(.pid | tostring == env.YABAI_PROCESS_ID)'"