Move tools, introduce helper to check if an output is available

• Move helpers.py to tools.py to avoid confusion with the introduction of helpers
• Introduce helpers folder for helpers used by clients developers
• Add helper to check if an output is available according to one unlock condition
  • with tests

---

• Are you ok with the naming tools.py?
• MyPy is not happy on the condition.left because it is defined as an empty string in the __init__(). I do not know how to overcome this.

duniterpy/helpers/money.py:18: error: "str" has no attribute "pubkey"
duniterpy/helpers/money.py:20: error: "str" has no attribute "time"
duniterpy/helpers/money.py:22: error: "str" has no attribute "timestamp"
duniterpy/helpers/money.py:24: error: "str" has no attribute "sha_hash"

Looks similar to https://github.com/python/mypy/issues/5719.

duniterpy/documents/crc_pubkey.py

@@ -4,7 +4,7 @@ import base58
 import re
 import hashlib
 from ..constants import PUBKEY_REGEX
-from ..helpers import ensure_str
+from ..tools import ensure_str
 
 # required to type hint cls in classmethod
 CRCPubkeyType = TypeVar("CRCPubkeyType", bound="CRCPubkey")