Bidirectional images and laser metadata

Support reading bidi images and laser metadata (#14)

* Allow reading bidirectional timeseries (assumes slices are z-aligned)

* Export BidiImageArray and test bidirectional image loading.

* Support reading laser information from Imagine header

Format updates

Merge pull request #11 from Cody-G/cjg/waveform_mode

Cjg/waveform mode

Fixes for Julia 0.6

Merge pull request #10 from timholy/teh/0.6

Updates for Julia 0.6

v0.3.1: Merge pull request #8 from timholy/teh/fix_noshift

Don't write "vertical shift speed" and "readout rate" if not defined

Fix z-axis pixel spacing

Merge pull request #7 from Cody-G/cjg/fix_dz

Fixed error in calculation of pixel spacing of the z axis: Because Im…

Upgrade to the new Images

This also changes the return type to N0f16. This will effectively rescale all array values by 1/65535.