in_lib: filter support

hello_filter.c

#include <unistd.h>
#include <fluent-bit.h>

int main()
{
    int i;
    int n;
    char tmp[256];
    flb_ctx_t *ctx;
    int in_ffd;
    int filter_ffd;
    int out_ffd;

    /* Initialize library */
    ctx = flb_create();
    if (!ctx) {
        exit(EXIT_FAILURE);
    }

    in_ffd = flb_input(ctx, "lib", NULL);
    flb_input_set(ctx, in_ffd, "tag", "test", NULL);

    filter_ffd = flb_filter(ctx, "stdout", NULL);
    flb_filter_set(ctx, filter_ffd, "match", "test", NULL);

    out_ffd = flb_output(ctx, "null", NULL);


    /* Start the background worker */
    flb_start(ctx);

    /* Push some data */
    for (i = 0; i < 100; i++) {
        n = snprintf(tmp, sizeof(tmp) - 1,
                     "[%lu, {\"key\": \"val %i\"}]",
                     time(NULL), i);
        flb_lib_push(ctx, in_ffd, tmp, n);
    }

    sleep(10);

    flb_stop(ctx);

    /* Release Resources */
    flb_destroy(ctx);

    return 0;
}