add features function + improve error handling

index.ts

src/features/burnToken.ts

src/features/createAssociation.ts

src/features/createProposal.ts

src/features/createToken.ts

src/features/joinAssociation.ts

src/features/showAssociationDetails.ts

src/features/showAssociations.ts

src/features/showBalance.ts

src/handlers/association/associationHandlers.ts

src/handlers/balance/balanceHandlers.ts

src/handlers/proposal/proposalHandlers.ts

src/handlers/roleHandlers.ts

src/handlers/token/tokenHandlers.ts

src/services/association.service.ts

src/services/proposal.service.ts

src/services/token.service.ts

test/handlers/association/associationHandlers.spec.ts

test/handlers/balance/balanceHandlers.spec.ts

test/handlers/proposal/proposalHandlers.spec.ts