merge profiling feature and document it

[cdetrio]

The profiling feature is in a branch: https://github.com/ewasm/scout/tree/profiling
And more features in a different branch: https://github.com/s1na/wasmi/tree/profile-invocations

Here's a script to format the profile output:

import sys
import re

profile_func_names = {}

for line in sys.stdin:
    func_names = re.match('^(\d+): (\S+)\n', line)
    func_times = re.match('^Function (\d+) took', line)
    if func_names:
        func_index = func_names.group(1)
        profile_func_names[func_index] = func_names.group(2)
    elif func_times:
        func_index = func_times.group(1)
        func_time_with_func_name = "{} {}".format(line.rstrip('\n'), profile_func_names[func_index])
        print(func_time_with_func_name)
    else:
        print(line.rstrip('\n'))

The output looks like this:

$ ./target/release/phase2-scout smptbvas.yaml | python scout_profile_parser.py
Process yaml!
blockdatasize 1612
blockdatacopy to 11520 from 0 for 1612 bytes
savepoststateroot from 13059
Total time taken 65612us
Function 35 took 40143us (61%) ethash_keccakf1600
Function 3 took 5246us (7%) ~lib/rt/stub/__alloc
Function 8 took 3024us (4%) ~lib/memory/memory.copy
Function 19 took 2629us (4%) ~lib/typedarray/Uint8Array#subarray
Function 25 took 2604us (3%) rlp/_decode
Function 14 took 1644us (2%) ~lib/array/ensureSize
Function 4 took 1313us (2%) ~lib/memory/memory.fill
Function 36 took 1180us (1%) keccak/ethash_keccak256
Function 12 took 936us (1%) ~lib/typedarray/Uint8Array#__get
Function 24 took 923us (1%) ~lib/array/Array<rlp/RLPData>#push
Function 17 took 915us (1%) rlp/Decoded#constructor
Function 13 took 872us (1%) ~lib/rt/stub/__realloc
Function 18 took 848us (1%) rlp/RLPData#constructor
Function 15 took 568us (0%) ~lib/array/Array<u8>#__set
Function 16 took 464us (0%) main/uintArrToNibbleArr
Function 20 took 410us (0%) ~lib/arraybuffer/ArrayBufferView#constructor
Function 37 took 394us (0%) f2_ethash_keccak
Function 32 took 370us (0%) main/verifyProof
Function 31 took 221us (0%) main/matchingNibbleLength
Function 28 took 217us (0%) ~lib/typedarray/Uint64Array#__get
Function 27 took 192us (0%) ~lib/array/Array<rlp/RLPData>#__get
Function 9 took 157us (0%) ~lib/rt/__allocArray
Function 7 took 83us (0%) ~lib/typedarray/Uint64Array.wrap
Function 30 took 60us (0%) ~lib/array/Array<u8>#slice
Function 26 took 39us (0%) rlp/decode
Function 29 took 35us (0%) main/getNodeType
Function 6 took 29us (0%) ~lib/arraybuffer/ArrayBuffer#get:byteLength
Function 21 took 24us (0%) ~lib/dataview/DataView#constructor
Function 22 took 22us (0%) ~lib/arraybuffer/ArrayBufferView#get:byteOffset
Function 33 took 18us (0%) main/main
Function 10 took 14us (0%) ~lib/array/Array.create<u8>
Function 11 took 1us (0%) ~lib/typedarray/Uint8Array.wrap
Function 5 took 1us (0%) ~lib/arraybuffer/ArrayBuffer#constructor
Function 23 took 1us (0%) ~lib/dataview/DataView#getUint16
Result: Some(I32(13059))
Execution finished