Expand tag support for Nikon

[tmclaugh]

Add greater tag support:

• Add missing standard tags
• Add more Nikon tags
• Fix some Nikon tags
• Handle pretty values for tags in multi-value lists

Not done:

• Handle pretty values for tags that use bit values.
• Simplify pretty values for tags with bitmasks
• Properly handle more SubIfds
  • StripOffsets(0x0111)
  • SubIfds (0x014A) - Not sure what this is yet.
• Nikon AFInfo2

Possible issues found.

• Byte fields return a string representation of the value instead of a string representation of the hex value