Merge pull request #3 from andreas-kupries/void-cast-clarification

Clarify the comment at the definition of IGNORE_RC.
Bug fix. Reset size information when clearing the history.

Otherwise the next historyAdd will access freed memory, and crash.
New feature: Accessor for the history max len.
New feature: Extended character transpose (Ctrl+t) at end of the line.

Bash is able to transpose characters with the cursor after the last
character. It simply transposes the last two. Added this behavior
to linenoise.