* mpi/mpicoder.c (mpi_read_from_buffer): Add word-size buffer
reading loop using 'buf_get_be(32|64)'.
(mpi_fromstr): Use look-up tables for HEX conversion; Add fast-path
loop for converting 8 hex-characters at once; Add string length
parameter.
(do_get_buffer): Use 'buf_put_be(32|64)' instead of byte writes; Add
fast-path for reversing buffer with 'buf_get_(be64|be32|le64|le32)'.
(_gcry_mpi_set_buffer): Use 'buf_get_be(32|64)' instead of byte reads.
(twocompl): Use _gcry_ctz instead of open-coded if-clauses to get
first bit set; Add fast-path for inverting buffer with
'buf_get_(he64|he32)'.
(_gcry_mpi_scan): Use 'buf_get_be32' where possible; Provide string
length to 'mpi_fromstr'.
(_gcry_mpi_print): Use 'buf_put_be32' where possible; Use look-up
table for HEX conversion; Add fast-path loop for converting to
8 hex-characters at once.
* tests/t-convert.c (check_formats): Add new tests for larger values.