[FIX] change handling of requestLedger options

ledger_index and ledger_hash were being set to true
instead of the specified value, and according to API
docs 'closed','validated', and 'current' can be
supplied to the ledger_index field to get the most
recent of the specified type
Merge pull request #176 from shekenahglory/develop

[FIX] change handling of requestLedger options
configurable maxAttempts
Merge pull request #178 from ripplerm/develop

configurable maxAttempts
[FEATURE] identity functions
[CHORE] vault client: add type to attest parameters
[TASK] vault client: add parameters to attest
[TASK] switch to new attestation endpoint
[FEATURE] vault client: update attestation and attestation summary
[TASK] vault client: tests for attestation routes and full summary
Merge pull request #181 from shekenahglory/feature/identity

Feature/identity
[DOC] update release notes