doc/api.rst: include private members of zpmlib.zpm
doc/api.rst: include private members of zpmlib.zpm

zerovm/zpm,zerovm/zerovm-cli,zerovm/zerovm-cli,zerovm/zerovm-cli,zerovm/zpm,zerovm/zpm,zerovm/zerovm-cli,zerovm/zerovm-cli,zerovm/zpm,zerovm/zpm,zerovm/zerovm-cli,zerovm/zpm