POSIX allows the default streams (stdin, stdout and stderr) to be
macros, which means that on such systems (musl libc is one) building
Lagom will fail due to the File::std*() names.
Also fix any files that use these identifiers.
Almost everyone using this API actually wanted String instead of a
ByteBuffer anyway, and there were a bunch of slightly different ways
clients would convert to String.
Let's just cut out all the confusion and make it return String. :^)
Grep supports only extended regular expressions, and is able to handle one pattern
handed over via -e or directly after the options. Also, multiple files can be
handed over. Recursive mode is outstanding, but no real magic :^)
