Ensure stream identifiers are limited to the correct character set

[jen20]

As of #21, stream identifiers are now structured, but represented on the wire as ByteString types. @jageall suggests that these should be limited in which bytes are acceptable, and that the encoding should then be ASCII rather than UTF-8 (though they are identical for the acceptable range of bytes). We should enforce this from the start in this client.

@jageall, what are the restrictions which need to be implemented here?

[jageall]

static readonly byte[] IllegalBytes = {
0x00,
0x01,
0x02,
0x03,
0x04,
0x05,
0x06,
0x07,
0x08,
0x09,
0x0A,
0x0B,
0x0C,
0x0D,
0x0E,
0x0F,
0x10,
0x11,
0x12,
0x13,
0x14,
0x15,
0x16,
0x17,
0x18,
0x19,
0x1A,
0x1B,
0x1C,
0x1D,
0x1E,
0x1F,
0x20,
0x21,
0x22,
0x23,
0x24,
0x25,
0x26,
0x27,
0x28,
0x29,
0x2a,
0x2b,
0x2c,
0x2f,
0x3a,
0x3b,
0x3c,
0x3d,
0x3e,
0x3f,
0x5b,
0x5c,
0x5d,
0x5e,
0x60,
0x7b,
0x7c,
0x7d,
0x7e,
0x7f
};

Anything above 0x7f is also considered illegal