Move closer to the standard autotools idiom. (#3187)

* Create `src/config.h` instead of passing everything on the compiler
  command line.

* To reduce the magnitude of this change, add `--include src/config.h`
  to CFLAGS instead of adding `#include "src/config.h"` at the top of
  each source file.  Not all compilers support this, but I don't think
  we care about anything other than gcc and clang at this point.

* Rather than generate `src/config_opts.inc`, emit `JQ_CONFIG` directly
  into `src/config.h`.

* Rather than generate `src/version.h`, define `JQ_VERSION` as an alias
  for the standard `PACKAGE_VERSION`.

.gitignore

@@ -18,7 +18,8 @@ jq.1
 
 # Generated source
 src/builtin.inc
-src/config_opts.inc
+src/config.h.in
+src/config.h
 *.pc
 
 # Autotools junk
@@ -38,8 +39,6 @@ jq-*.zip
 configure
 aclocal.m4
 Makefile.in
-version.h
-.remake-version-h
 config.cache
 *.rpm
 m4/libtool.m4