Revert "Merge branch 'rewrite'"

This reverts commit 4b86e002677d66b6da9943ef7a044a9366a41c45, reversing
changes made to 036a982f9ee332fd6f8f7da5674c6c412bcb246d.

Conflicts:
	src/utp/lib.rs
Revert "Merge branch 'performance'"

This reverts commit 7d1f44022a423413fa2305489924328b2b1ca50a, reversing
changes made to 3133d37c062e913d76a9bf54f42ed1e7d1a88571.

Conflicts:
	src/utp/lib.rs
Revert "Merge branch 'performance'"

This reverts commit 1756655a78a11a8db22553be80ebe1632d2b70f4, reversing
changes made to 0af3f1be20bf81eff56163b0daaff0493a49f404.

Conflicts:
	src/utp/lib.rs
Simplify pending data flushing.
Slightly cleaned up code.
Merge branch 'safety'
Update README.