Remove trailing whitespaces for zero-operand instructions

Thanks jrfonseca
Change doc install directory to datadir/udis86

Thanks to Roi Martin
Fixes for assembly output buffer

As pointed out by Andrew Sveikauskas (https://github.com/asveikau),
mkasm does not check for overflows. This change address the overflow
issue in a simple way, by dropping/truncating the output and increasing
the buffer size to 128 chars to accomodate most common cases. If a
client anticipates larger output requirements, the change adds a new
interface ud_set_asm_buffer, that can switch to a user buffer. The
behavior is still the same, output is truncated on overflow.
Add support for client symbol resolver

Add support for symbol resolution by the client. The client can
register a call back function that may return a symbol+offset for a
given target address. This is based on Dmitry Stogov's (dstogov) patch
and further comments from Andrew Sveikauskas.(asveikau)
Ignore sym_resolver binary