Single point for ldd, make ELF.libs and SSH.libs return consistent output

Single point of code for `ldd`, make ELF.libs and SSH.libs return consistent output of `{full local path: ldd address}`

Moved `pwn.elf.ldd` to `pwn.utils.misc` to replace `pwn.utils.misc.parse_ldd_output`.

This is a diversion from the legacy output of `ssh.libs`, which returned a dict of `{soname: full local path}`.

```python
>>> from pwn import *

>>> ELF('/bin/bash').libs
{'/lib/x86_64-linux-gnu/libc.so.6': 140737345654784,
 '/lib/x86_64-linux-gnu/libdl.so.2': 140737349615616,
 '/lib/x86_64-linux-gnu/libtinfo.so.5': 140737351729152}

>>> ssh(host='vortex.labs.overthewire.org',user='vortex1',password='Gq#qu3bF3').libs('/bin/bash')
{'/home/user/pwntools/vortex.labs.overthewire.org/lib/x86_64-linux-gnu/libc.so.6': 140737345781760,
 '/home/user/pwntools/vortex.labs.overthewire.org/lib/x86_64-linux-gnu/libdl.so.2': 140737349718016,
 '/home/user/pwntools/vortex.labs.overthewire.org/lib/x86_64-linux-gnu/libtinfo.so.5': 140737351831552}
```

It also works for BSD without warnings (I'd previously contributed a [work-around](https://github.com/Gallopsled/pwntools/pull/32/files#diff-1) for `parse_ldd_output`).

```py
>>> from pwn import *
>>> shell=ssh(host='bsd.binjit.su',user='user')
>>> shell.run_to_end('uname -a')
('FreeBSD bsd.binjit.su 10.0-RELEASE FreeBSD 10.0-RELEASE #0 r260789: Fri Jan 17 01:46:25 UTC 2014     root@snap.freebsd.org:/usr/obj/usr/src/sys/GENERIC  i386\n', 0)
>>> shell.libs('/usr/local/bin/bash')
{'/home/user/pwntools/bsd.binjit.su/usr/local/lib/libintl.so.9': 672493568,
 '/home/user/pwntools/bsd.binjit.su/lib/libncurses.so.8': 672247808,
 '/home/user/pwntools/bsd.binjit.su/lib/libc.so.7': 672530432}
```