lib/pattern: add set of functions to parse combined pattern input

lib/pattern: add set of functions to parse combined pattern input

The idea of this patch is to have several helpers to parse combined
pattern input, which can consists of strings, numbers and formats.

For example now pattern can be combined and look like this string:

 input : 0xdeadbeef"123"0xdeadface
 output: de ad be ef 31 32 33 de ad fa ce

  or

 input : -99"some string"0x66
 output: 9d ff ff ff 73 6f 6d 65 20 73 74 72 69 6e 67 66

  or with formats

 input : 0xdeadface0xffff%o
 output: de ad fa ce ff ff 00 00 00 00 00 00 00 00

 where %o - offset of the block, reserved 8 bytes

 Space for formats is reserved in output buffer.
 When buffer will be ready to be written to disk - 'paste' callback
 should be called for each pattern format. Each callback is responsible
 for writing data inside the reserved space in the output buffer.

Format array can be extended at any time, all you need is to provide
the name of the format and correct 'paste' callback.

Signed-off-by: Roman Pen <r.peniaev@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>