Audit Revision v0.2.0-alpha

Address all issued raised in audit report

Changelog

• Removed solmate dependency (fixes #31, #33, #37)
• fix: overflow situation #30
• fix: data consistency #32
• fix: unchecked transfer #34
• fix: check-effects-interaction #35
• refactor: standard to revert with custom errors (#47)
• refactor: standardise Pragma version #36
• refactor: style guide & function modifiers (#45 #39 #46 #44)
• style: finished NatSpec #53
• tests: negative cases (#57 #42)