first attempt at npyappend package

[ggggggggg]

This isn't ready to go yet, but I want to share how far I got.

Good:

• Can append single values of float32 and float64 and slices of uint16.
• Can refresh the header.
• Tests check the above functionality.

Todo:

• Test uint16 values are correct.
• Write speed optimizations.
  • Use getbytes (I have a draft in Append2)
  • Have a write buffer of some sort. (You could probably use a buffered writer on the file for appending, and just seek back and forth without the buffered writer's knowledge, or just implement our own buffered write function.)
  • Have a way to write a whole pulse record into multiple files of this format.

Bad/learning:

• I tried tried to use arrays so that you couldn't pass the wrong length, but that didn't work well. It would probably be annoying in practice in go as well.
• I used generic types, but this may have been a bad idea because Go doesn't have many tools for them.
• OMG I can't believe how much verbose error handling boiler plate there is in go.