Coerce crs input as necessary

[anthonynorth]

Reverts strict crs type requirement for proj strings.

Fixes #52

[anthonynorth]

Should we notify when crs input is changed? I.e. if crs is a proj string, but +type=crs is absent, should we message() / warning()?

Should I move this logic to c?

Edit: a working c implementation below. If we're certain proj strings are always small, we could stack allocate the new_crs buffer.

static bool str_starts(const char* str, const char* pre) {
  return strncmp(pre, str, strlen(pre)) == 0;
}

static bool str_contains(const char* str, const char* test) {
  return strstr(str, test) != NULL;
}

PJ* proj_create_crs(PJ_CONTEXT* ctx, const char* crs) {
  if ((str_starts(crs, "proj=") || str_starts(crs, "+proj=") ||
       str_starts(crs, "+init=") || str_starts(crs, "+title=")) &&
      !str_contains(crs, "type=crs")) {

    const char* type = " +type=crs";
    size_t sz = strlen(crs) + strlen(type) + 1;
    char* new_crs = malloc(sz);

    snprintf(new_crs, sz, "%s%s", crs, type);
    PJ* crs_obj = proj_create(ctx, new_crs);
    free(new_crs);

    return crs_obj;
  }

  return proj_create(ctx, crs);
}

// with usage : proj_create_crs(ctx, crs_str);

[mdsumner]

lgtm! fixes the problem I had