Added check that parameter name matches fully

[olekhov]

Hello. I've encountered m3u8 playlist with custom header: #EXT-X-MEDIA-READY:7f659f6f09bce196d7 This header is erroneously parsed as #EXT-X-MEDIA header and gives this error: ValueError: not enough values to unpack (expected 2, got 1) at parser.py: 275

I think you should check that parameter string starts with exact parameter name, not just part of it. Here is PR that fixes this. test is also provided.