Several new functions and a remote file type

Here are several functions that ease the use of hashes and help us to use them to a greater advantage. 
Three of the functions allow us to retrieve subsets of an nested hash based on it's children. 
The fourth functions allows us to prefix the keys of an hash, most commonly used to prefix the hostname if a hash is used to create exported resources (f.e. nagios checks)

I also included a remote_file type that is used to fetch files from an url.