chore(readme): update readme and code clean up

Author: apaparazzi0329

MIGRATION-V11.md

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+# v11.0.0 Migration Guide
+
+### Breaking changes by service
+
+#### Assistant v2
+- Model `MessageContext` property `skills` type changed to new `MessageContextSkills`
+- Model `Environment` property `language` removed
+- Model `EnvironmentReleaseReference` renamed to `BaseEnvironmentReleaseReference`
+- Model `EnvironmentOrchestration` renamed to `BaseEnvironmentOrchestration`
+- Model `SkillReference` renamed to `EnvironmentSkill`
+
+#### Discovery v2
+- Parameter `smartDocumentUnderstanding` removed from `CreateCollectionOptions`
+- Model `QueryResponsePassage` and `QueryResultPassage` property `confidence` removed
+- QueryAggregation models restructured
+
+#### Natural Language Understanding
+- All `sentimentModel` functions removed
+
+#### Speech to Text
+- `AR_AR_BROADBANDMODEL` model removed in favor of `AR_MS_BROADBANDMODEL` model
+
+
+### New Features by Service
+
+#### Assistant v2
+- `createAssistant` function
+- `listAssistants` function
+- `deleteAssistant` function
+- `updateEnvironment` function
+- `createRelease` function
+- `deleteRelease` function
+- `getSkill` function
+- `updateSkill` function
+- `exportSkills` function
+- `importSkills` function
+- `importSkillsStatus` function
+- Improved typing for `message` function call
+See details of these functions on IBM's documentation site [here](https://cloud.ibm.com/apidocs/assistant-v2?code=node)
+
+#### Discovery v2
+- Aggregation types `QueryTopicAggregation` and `QueryTrendAggregation` added
+
+#### Speech to Text
+- added `FR_CA_MULTIMEDIA`, `JA_JP_TELEPHONY`, `NL_NL_MULTIMEDIA`, `SV_SE_TELEPHONY` models
+
+#### Text to Speech
+- added `EN_AU_HEIDIEXPRESSIVE`, `EN_AU_JACKEXPRESSIVE`, `EN_US_ALLISONEXPRESSIVE`, `EN_US_EMMAEXPRESSIVE`, `EN_US_LISAEXPRESSIVE`, `EN_US_MICHAELEXPRESSIVE`, `KO_KR_JINV3VOICE`
+- Parameters `ratePercentage` and `pitchPercentage` added to `synthesize` function
+See details of these new parameters on IBM's documentation site [here](https://cloud.ibm.com/apidocs/text-to-speech?code=node#synthesize)