add bap-mc

This adds a first-pass of the `bap-mc` utility for disassembling hex strings, similar to `llvm-mc`.

`echo "0x48 0x83 0xec 0x08 0xe8 0x47 0xee 0xff 0xff 0x8b 0x40 0x10 0x48 0x83 0xc4 0x08 0xc3" | ./bap-mc --show-asm --show-inst`
```
    (SUB64ri8 r:44 r:44 0x8)                          ; subq    $0x8, %rsp
    (CALL64pcrel32 -0x11b9)                           ; callq   -0x11b9
    (MOV32rm r:19 r:35 0x1 r:0 0x10 r:0)              ; movl    0x10(%rax), %eax
    (ADD64ri8 r:44 r:44 0x8)                          ; addq    $0x8, %rsp
    (RET)                                             ; ret
```

`echo "e1 e2 50 50 00 11 a0 10 04 15 9f 00 10 1b ff 93 04 e1 a0 00 05 e2 8d d0" | bap-mc --show-inst --arch=arm --show-asm`
```
    (SUBrsi r:10 r:66 r:67 0x2c 0x5 r:3 r:3)                         ; subspl   lr, r0, r1, ror #5
    (ADCrsi r:67 r:66 r:66 0x12 0x1 r:3 r:0)                         ; adcne    r1, r0, r0, lsl #2
    (ADDrsi r:67 r:11 r:70 0x52 0x0 r:3 r:3)                         ; addseq   r1, pc, r4, lsl #10
    (LDR_POST_IMM r:11 r:69 r:69 r:0 0x24f1b 0x0 r:3)                ; ldreq    pc, [r3], #3867
    (STRi12 r:76 r:66 0xffffff1f 0x0 r:3)                            ; streq    r10, [r0, #-225]
```

`echo "e1 e2 50 50 00 11 a0 10 04 15 9f 00 10 1b ff 93 04 e1 a0 00 05 e2 8d d0" | bap-mc --show-inst --arch=arm --show-asm --show-kinds --imm-format=dec --reg-format=name`
```
    ;; may_load, may_store
    (SUBrsi LR R0 R1 44 5 CPSR CPSR)                                 ; subspl   lr, r0, r1, ror #5
    ;; may_load, may_store
    (ADCrsi R1 R0 R0 18 1 CPSR nil)                                  ; adcne    r1, r0, r0, lsl #2
    ;; may_load, may_store
    (ADDrsi R1 PC R4 82 0 CPSR CPSR)                                 ; addseq   r1, pc, r4, lsl #10
    ;; may_affect_control_flow, may_load, may_store
    (LDR_POST_IMM PC R3 R3 nil 151323 0 CPSR)                        ; ldreq    pc, [r3], #3867
    ;; may_load, may_store
    (STRi12 R10 R0 4294967071 0 CPSR)                                ; streq    r10, [r0, #-225]
```
It is installed as `bap-mc`. The name was chosen to be consistent with `llvm`, and as a more widely adopted convention on unix system.