TODO:
* add support for extended attributes
** check v1 and v2 attributes
** add support for reading v5 remote attribute value data blocks

* complete basic format version 4 and 5 support
** complete libfsxfs_file_entry_get_sub_file_entry_by_utf8_name
** complete libfsxfs_file_entry_get_sub_file_entry_by_utf16_name

* for extended attributes by name look up use native XFS B+ tree structures

* implement or remove libfsxfs_file_entry_is_empty from info_handle

* move code to read directory table entry into directory entry?

* store (directory table) parent inode number in directory entry?

* change btree_block into btree_node

* add support for XFS_SB_VERSION_BORGBIT

* add support for format version 1 (need test data)
* add support for format version 2 (need test data)
* add support for format version 3 (need test data)

* create test data with unwritten extent

* determine if out of order extents are allowed, create test data

20200105
* see `git log' for more recent change log
* Initial version

