Configurable timeout on build(), defaults to None

Many commands used in Dockerfiles hang for an extended period of time
without producing any output, which will result in a socket timeout.
Accordingly, it makes sense for build() to specify no timeout by
default.
Break down _post() parameters one-per-line in build()
Merge pull request #139 from aanand/no-timeout-on-build

Configurable timeout on build(), defaults to None