Implement new FHIRPath operators and functions

What's Changed

New Features & FHIRPath Operators

This release introduces a significant number of new FHIRPath operators and functions.

• Implement for memberOf by Zihan Chen (@zihanchen) (#26)
• Implement for split by Zachary Sylvia (@zsylvia-verily) (#26)
• Implement for SupersetOf by Vikas Gogia (@gogiavikas) (#26)
• Implement resolve by Marwan Tammam (@Quarz0) & integrated by Vicknesh Suresh (@VickSuresh) (#27)
• Implement repeat by Marwan Tammam (@Quarz0) & integrated by Alexander Sullivan (@AlexJSully), Alexandre Laurin (@alexlaurinmath) and Matthew Rodusek (@bitwizeshift) (#31)
• Implement trace by Matthew Rodusek (@bitwizeshift) (#36)
• Implement | (union), contains and in operators by Marwan Tammam (@Quarz0) & integrated by Alexandre Laurin (@alexlaurinmath) (#25)
• Implement hasValue and as by Marwan Tammam (@Quarz0) & integrated by Alexander Sullivan (@AlexJSully) (#30)

Enhancements

• Added list of resource types with canonical URL by Bikram Kashyap (@biki23) (#26)
• Add MaybeVersionedURI and MaybeVersionedURIString to FHIR resource by Daniel Han (@YoungInHan) (#26)
• Update for handling extensions by Bharath Vemula (@bharath-v1) (#33)

Bug Fixes

• Fixed a bug in FHIR methods by Daniel Han (@YoungInHan) (#26)
• Fixed some FHIRPath expression evaluation issues by Marwan Tammam (@Quarz0) & integrated by Alexander Sullivan (@AlexJSully) (#28)

Maintenance & Dependency Updates

• Timezone related methods are missing unit tests by Alexander Sullivan (@AlexJSully) (#26)
• Code clean-up by Alexander Sullivan (@AlexJSully) (#29)
• Go version and packages update by Arthur Pang (@arthurpang) (#33)
• Go decimal package update by Joel Phillip (@joelphillip1) (#33)

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Full Changelog: v1.4.0...v.1.5.0