Functional changes

Linux support added (tested under Ubuntu 20.04.3). From this version onwards, binaries for Linux on x86-64 will also be provided for versioned releases. Some more general code portability provisions have also been made.
drat inspect now automatically detects the APFS block size, based on the block size value provided by the container superblock found at block 0.
Extended fields (xfields) are now supported.
drat recover now gets the actual file size and thus outputs files of the correct size rather than a multiple of the APFS block size. The tools in /supplemental-tools have thus been removed. (Issue #2).
UUIDs are now printed in standard format.
Fixed bug in get_nx_incompatible_features_string() and get_nx_flags_string() that caused these functions to analyse the nx_features field instead.
drat version now outputs legal info (copyright notice, warranty, and licence).

Other changes

Refactored libraries:
- /include has been added to the compilation include path to avoid use of relative paths.
- /src/apfs/struct has moved to /include/apfs, and can thus be included as <apfs>. This library contains headers that define all data structures detailed in Apple's APFS specfication.
- The remainder of /src/apfs has moved to /include/drat, and can thus be included as <drat>. This library contains functionality specific to Drat:
  - Headers in <drat/func> define functions that facilitate common operations on data strctures provided by <apfs>;
  - Headers in <drat/string> define functions that produce human-readable strings/output detailing the data contained in data structures provided by <apfs>; and
  - Headers in <drat> define miscellaneous functions.
Refactored code:
- String generation functions that operate on enum fields have had their shared code factored into <drat/string/common.h> as get_single_enum_string() and get_flags_enum_string().
- Use of ctime() for printing timestamps has been factored into get_apfs_timestamp_string().
Documentation for v0.2.x has been drafted in /docs using Sphinx.