Check channels match data when writing

[kretep]

Currently, it's possible to define any set of channels for any data, which results in errors when reading back. We should check whether the channels match the data when writing (either when writing the binary, when metadata is passed, or when writing the metadata)

[kretep]

Also, the "writing data from scratch" section in the docs has this problem

[vedran-kasalica]

          Verify the fields (including channels and units) when writing the TSDF data.

Also posted by @vedran-kasalica in #39 (comment)