Load
====
Photoshop 2.0 and lower files are not supported due to lack of 
file specs and test files.

Add text names for colour modes

Use tiles for image load

Use tiles for layer load

Parasite for layer blending ranges per channel?

Read & use global mask data

Check for block over-run in read_channel_data

Invert layer mask - channel_set_show_masked or invert mask + parasite

decode more image resources

Read in layer resources and process adjustment layers etc.
add parasites as required - should be similar to image resources

add layer support for:
luni - unicode name.		ps 5
lyid - Layer ID (tattoo)	ps 5


Image resources:
================

1005 - resolution
  width and height units dropped.

1007 - Display info
  save colour space & colour as parasite.

1008 - caption - Add to XMP data block.

1024 - Layer state
  loaded but unused - requires tattoos from layer resource info (lyid).

1033 1036
  Better error handling for Jpeg decompression. Check for JPEG being included

2000-2998 - Paths
  Add initial fill rule and clipboard parasites.

2999 - Clipping path
  Add as parasite to path record.