remove std.fs.Dir.readFileAllocOptions, replace with more flexible API
readFileIntoArrayList
remove std.fs.File.readToEndAllocOptions, replace with more flexible API
readIntoArrayList
update std.fs.File to new reader/writer API
add helper functions to std.io.Reader.Limit
replace std.io.Writer.FileLen with std.io.Reader.Limit
make offset a type rather than u64 so that it can distinguish between
streaming read and positional read
avoid an unnecessary allocation in std.zig.readSourceFileToEndAlloc when
there is a UTF-16 little endian BOM.
Simplifies code in docs creation where we used `std.tar.output.Header`.
Writer uses that Header internally and provides higher level interface.
Updates checksum on write, handles long file names, allows setting mtime and file permission mode. Provides handy interface for passing `Dir.WalkerEntry`.
Now that `-femit-docs` includes all modules, including the builtin
module, in the generated source tarball, it makes sense to apply the
same logic to the std-docs server. std-docs constructs its own tarball,
so a different approach is needed to achieve the same end result.
