Breaking changes

Enums variants using #[br(magic)] with mixed data types (i.e. enum Foo { #[br(magic(0_u8))] A, #[br(magic(1_i16))] B }) will now always parse top-to-bottom. Previously, variants would be parsed in groups by type. To maximise performance when parsing enums with mixed magic types, make sure variants with the same magic data type are contiguous. (Thanks, @MrNbaYoh!)
The BinrwNamedArgs macro and trait have been renamed to NamedArgs.
The ReadOptions::offset field has been moved and is now a named argument specific to the FilePtr type. The #[br(offset)] and #[br(offset_after)] directives will continue to work without any change, but manual uses of FilePtr must now pass the offset in arguments instead of options.
ReadOptions and WriteOptions have been removed and replaced with a single Endian parameter.
The Args associated type now takes a lifetime to support borrowed arguments. Custom helper functions that don’t need to support borrowed arguments can use the 'static lifetime to maintain the previous behaviour.

New features

The #[br(dbg)] directive can be used for quick and dirty debugging output to stderr. (Thanks, @Swiftb0y!) (#50, #162)
The args_iter helper can be used for parsing any field where each item is parsed using a value from another iterator as an argument (e.g. an object containing a list of header entries, followed by a list of body entries, where each body entry requires data from the corresponding header entry to be parsed.)
The TakeSeek reader adapter is a seekable version of the std::io::Take adapter. Use it by importing the TakeSeekExt trait and calling take_seek on any Read + Seek stream.
The #[binrw::parser] and #[binrw::writer] attributes simplify the creation of functions compatible with the parse_with and write_with directives.
The #[brw(try_calc)] directive adds a fallible version of the existing calc directive.
Add directives for accessing and remapping streams by @csnover in #174 (#[brw(map_stream)])

It is now possible to use references in imports/arguments.
Rendering of errors can now be controlled using the verbose-backtrace crate feature (enabled by default). Disabling this feature removes extra decorations, ANSI codes, and source text from the built-in error formatting.
The no-std implementation of Cursor now overrides Seek::stream_position for improved performance using that API.
More useful error messages are now given when an args directive is missing from a field that requires it. (#67, #76)
Combining #[binread] and #[binwrite] on a struct or enum is now equivalent to just using #[binrw]. Previously, this was an error.
Assertion failures without explicit error messages in #[br(assert)] directives now cause clearer error messages that explicitly state that an assertion failed. Previously, only the expression that failed to assert was given in the output.

The no-std implementation of Cursor now actually seeks when using SeekFrom::End.
End-of-file I/O errors are now correctly detected in all cases. (#125)
#[br(try)] now only constructs a default value when parsing actually fails.
Errors in assert, count, offset, offset_after, and parse_with directives now point correctly at the source of the error.