Option to elide space between value and units

[mcandre]

Please include an option to remove spaces between values and units.

[dustin]

This came up in #32 as a response to #21 where we (slightly reluctantly) decided to comply with SI standards. If you wish to deviate, it makes sense to write a small space absorbing wrapper.

There's no natural place for options now, so we'd have to make a new API just to deal with non-standard presentations that can easily be done by creating a local API that absorbs space (e.g., here's an example io.Writer that eats spaces).