Refactor read_and_print_args switch to use less copy/paste
Don't mention 'no Devel::Trace::Syscall' in docs

use Devel::Trace::Syscall doesn't make sense either, since
this is a debugger module
Mention the locale data bug in the CAVEATS
Remove unused variable
Change bytes_read type to squash warning
Fix field initializer errors with gperf code
Change name of 'struct syscall'
Remove TODO comments

I've got these written down elsewhere
Rename my_custom_signal to syscall_occurred
Comment our globals

Normally I believe in self-documenting variables, but since the globals
are shared between the child and parent processes, I wanted to explain
who uses what
Rename syscall-hash.h to syscall-lookup.h