db-add: replaced std::endl with '\n'

tools/Generic.hpp does no longer pull std::endl into the auris::tools namespace (removed 'using std::endl'). This should encourage tools to not use endl, but rather '\n' for consistency. Windows won't be happy, but that's life.
Generic tool: print_usage and usage_string const

The functions print_usage() and usage_string() of tools/Generic.hpp are now declared const. Pure cosmetics, but meh - beautiful code, beautiful app.
fixed db file Track hanging upon read

When reading a track file, the db::file::Track class' read() function would hang due to it entering an infinity loop when attempting to skip empty lines (is.peek() called without subsequent is.get()). An additional is.peek() at the end of the loop ensures that an EOF is caught properly.

Also made the exception text more descriptive.
fixed Track read logic for format field

The read() function of db/file/Track.hpp does not properly read the format field of each format line. The buffer is filled immediately with characters, even those that are still in ctmp and might be part of the double hyphen separator (' -- ').

This commit fixes this by moving characters into the format buffer only after they drop out of the ctmp ringbuffer.
added db-meta command

Added db-meta.cpp which implements a command that allows for track metadata to be displayed (implemented) and modified (not implemented).