add more conversions for Value #189

Job	Run time
Check Semantic Versioning	2m 34s
Check Minimum Rust Version	21s
Unit Tests (stable, default)	44s
Unit Tests (stable, bigint)	52s
Unit Tests (stable, serde1)	52s
Unit Tests (stable, fraction1)	52s
Unit Tests (stable, rand1)	46s
Unit Tests (stable, bigint,serde1,fraction1,rand1)	59s
Unit Tests (beta, default)	41s
Unit Tests (beta, bigint)	51s
Unit Tests (beta, serde1)	52s
Unit Tests (beta, fraction1)	46s
Unit Tests (beta, rand1)	46s
Unit Tests (beta, bigint,serde1,fraction1,rand1)	58s
Unit Tests (nightly, default)	41s
Unit Tests (nightly, bigint)	50s
Unit Tests (nightly, serde1)	48s
Unit Tests (nightly, fraction1)	46s
Unit Tests (nightly, rand1)	42s
Unit Tests (nightly, bigint,serde1,fraction1,rand1)	55s
	17m 36s

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