Use warn/croak instead of Perl_warn/croak

The latter doesn't work on interpreters built with multiplicity
enabled
Remove define for WORD

Turns out I don't use this!
Fix alignment of globals that we touch with ptrace

Most compilers will probably align these on word boundaries
as it is, but it doesn't hurt to be specific
Write trace info to standard error
Inline read_event

It was really a dumb wrapper around fread, and not necessary
Add a bunch of argument formatting for nullary syscalls
Add formatting for many other system calls

This is pretty rudimentary, but should give us a decent start