Add 16bit dithering for 256/16M rgb console + fixes

Add scr.rgbcolor to disable 16bit ansi escapes
Disabled by default on windows
Implement ansi to rgb and rgb to ansi conversors
Implement 256 color to rgb bruteforcer
ec: renamed to ecr
Fixes for the VE menu
Drop --enable-devel flag from r2-bindings/README
Add 'floc' and 'invalid' color palettes, Vdr renames locals

Vdr now support renaming local function labels
Do not colorize lines when scr.color=0
Fix #150 IO issue.
Better comments in disasm, fix io->size = 0 regression
Bring back code|data xrefs to life. Use 'ar' command

'ax' and 'ar' are in conflict. must resolve
Uses sdb to store code and references
Ugly code that needs a huge cleanup
Update to latest sdb
r_bin: removed rva, offset and size from imports.

PLT-like lazy import wrappers are now part of symbols, where applicable.
The "imp." prefix is a temporary solution, it should be a flag.
r_bin: removed hint from RBinImport, as it's only used in PE and even there it's doubtfully relevant.
r_bin/ELF: don't ignore the r_addend field from Elf_Rela relocs.
r_bin: new generalized relocs, with only arch-independent types.

Basic implementation for ELF relocs (x86, x64 and ARM).
r_bin/PE: implement new relocs.
Mach-O: new relocs implementation and complementary fixes for imports.
r_bin/mach0: updated mach0_specs.h using original Apple headers where possible.
r_bin/mach0: new relocs using dyld_info bind opcodes.