Add a new helper file 'tools.c' that provides some useful APIs

This patch borrows the 'tools.c' helper file from the crash utility
project and adds it to the makedumpfile source code, to allow
some basic useful APIs to be present which can be invoked from
other source code files.

'tools.c' provides some useful APIs like 'htol' (convert
a string to a hexadecimal long value), etc. which can be
invoked by other functions (a functionality that is exposed
by follow-up patches).

Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>