refactor: better error check(that handle wrap), use std constants, typos and fields alignement

[GreyXor]

• Correction of some small spelling mistakes.
• Better error wrapping print/check by using %w and Error.is(...).
• Save 80 bytes in structs by aligning the padding fields.
• Using std constants.

fieldalignment -fix .
/home/greyxor/Documents/Projects/sse/client.go:42:13: struct with 128 pointer bytes could be 120
/home/greyxor/Documents/Projects/sse/server.go:17:13: struct with 56 pointer bytes could be 32
/home/greyxor/Documents/Projects/sse/stream.go:14:13: struct with 136 pointer bytes could be 96
/home/greyxor/Documents/Projects/sse/subscriber.go:10:17: struct with 40 pointer bytes could be 32

[portante]

Seems like a solid set of changes. Any reason for not merging this?

[GreyXor]

I switched to https://github.com/tmaxmax/go-sse