. size overflows, just don't do it (tm) ... (Ie. having a Vstr string of
  length (SIZE_MAX - 1) and adding 2 bytes to it will just break.

. vstr_conv_*_uri() sucks if it's not the entire string.

. vstr_export_cstr_buf() should take a char* not a void*.

. vstr_srch_chrs_fwd() etc. should probably take a void* not a char*.

. wchar_t support is there because the std. printf() requires it ... it only
  works if your OS supports wcrtomb() (FreeBSD-4.6 doesn't) and that means that
  the locale information is process local, not string local ... as other
  locale information is.