Implemented regex match execution.

src/lib-sieve/plugins/regex/ext-regex.c

src/lib-sieve/plugins/regex/regex.sieve

src/lib-sieve/plugins/relational/ext-relational.c

src/lib-sieve/sieve-address-parts.c

src/lib-sieve/sieve-address-parts.h

src/lib-sieve/sieve-common.h

src/lib-sieve/sieve-match-types.c

src/lib-sieve/sieve-match-types.h

src/lib-sieve/tst-address.c

src/lib-sieve/tst-header.c