revset: add parsing rule for key=value pair
It will be used as an keyword argument.
Note that our "=" operator is left-associative. In general, the assignment
operator is right-associative, but we don't care because it isn't allowed to
chain "=" operations.
FROM debian:jessie
RUN apt-get update && apt-get install -y \
build-essential \
debhelper \
dh-python \
devscripts \
python \
python-all-dev \
python-docutils \
zip \
unzip