Implement SRFI-43 Vector Library.

Implement SRFI-43 Vector Library.

* module/srfi/srfi-43.scm: New file.
* module/Makefile.am (SRFI_SOURCES): Add module/srfi/srfi-43.scm.
* test-suite/tests/srfi-43.test: New file.
* test-suite/Makefile.am (SCM_TESTS): Add test-suite/tests/srfi-43.test.
* doc/ref/srfi-modules.texi (SRFI-43, SRFI-43 Constructors)
  (SRFI-43 Predicates, SRFI-43 Selectors, SRFI-43 Iteration)
  (SRFI-43 Searching, SRFI-43 Mutators, SRFI-43 Conversion): New nodes.