added mapfile aux functions

Added the aux/mapfile.hpp file which contains a collection of helper functions that allow a file to be read or written in its entirety. Currently reading and writing from/to std::ostream and std::string is supported, with each function coming in two flavors:
- bool return value that returns false if the file cannot be opened; or
- void return value that throws an exception
db-meta: comment line of output now in stderr

The comment line at the top of db-meta's output ("# track ...") is now printed to standard error. This makes it visible to the user but keeps the output clean, making the tool's output more easy to use.
db-add: removed --list option

Removed the --list option from the db-add tool. Also removed the now unused ctime header include.
added db-list tool

Added the db-list.cpp tool that lists a database's track index. This is basically and extracted version of the listing code from db-add.cpp, but now using the aux/mapfile functions to make the code more readable.added db-list tool.