Implement more search commands

[radare]

Other useful / commands to have in r2frida:

• [x] /v[1,2,4,8] will be also nice
• [ ] /c -- disassemble until instruction matches given string
• [ ] /R -- search for ROP gadgets (implement rop.js ?)
• [ ] /r -- search for references to address
• [ ] /V min max -- find value in range
• [x] /w -- wide string (done but not working)
• [x] /z -- https://github.com/nowsecure/r2frida/issues/92

[trufae]

cc @mrmacete