read.im3d now adds input file as an attribute

* closes #131
doc: document core attributes of im3d
fix example of reading vaa3d raw image

should use read.im3d not the read.vaa3draw.im3d function
Teach read.im3d to read amiramesh files without standard extension
test reading of amiramesh file without standard extension
Bump version to 1.5.5