Added readline support for linux/osx

[sludin]

Added support for readline to provide command history and smoother terminal handling. I could not find a reasonable version for windows, nor do I have a windows dev environment so I created a stub version for _WIN32 using the existing get_line function as a base with tweaks as readline returns malloc'd memory.

[MMitsuha]

https://github.com/caizhe666/mcrconpp

see this for auto completion