Add HTTP/HTTPS Fetch() API to redbean

You can now say the following in your redbean Lua code:

    status,headers,payload = Fetch("https://foo.example")

The following Lua APIs have been introduced:

  - Fetch(str) → str,{str:str},str
  - GetHttpReason(int) → str
  - GetHttpReason(int) → str
  - ProgramSslFetchVerify(bool)
  - ProgramSslClientVerify(bool)

The following flags have been introduced:

  - `-j` enables client SSL verification
  - `-k` disables Fetch() SSL verification
  - `-t INT` may now be passed a negative value for keepalive

Lua exceptions now invoke Cosmopolitan's garbage collector when
unwinding the stack. So it's now safe to use _gc() w/ Lua 𝔱𝔥𝔯𝔬𝔴

See #97

net/http/unchunk.c

@@ -43,7 +43,7 @@ ssize_t Unchunk(struct HttpUnchunker *u, char *p, size_t n, size_t *l) {
         if ((h = kHexToInt[c]) != -1) {
           u->m *= 16;
           u->m += h;
-          if (u->i + u->m >= n) return ebadmsg();
+          if (u->m >= 0x0000010000000000) return ebadmsg();
           break;
         }
         u->t = kHttpStateChunkExt;