Better error messages on ErgoTree evaluation

[greenhat]

Close #353

[coveralls]

Pull Request Test Coverage Report for Build 6324467950

• 705 of 1132 (62.28%) changed or added relevant lines in 90 files are covered.
• 14 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-1.9%) to 81.06%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
ergo-lib/src/chain/transaction/reduced.rs	4	5	80.0%
ergotree-interpreter/src/eval/create_prove_dh_tuple.rs	0	1	0.0%
ergotree-interpreter/src/eval/create_provedlog.rs	0	1	0.0%
ergotree-interpreter/src/eval/decode_point.rs	1	2	50.0%
ergotree-interpreter/src/eval/deserialize_register.rs	5	6	83.33%
ergotree-interpreter/src/eval/expr.rs	19	20	95.0%
ergotree-interpreter/src/eval/extract_reg_as.rs	1	2	50.0%
ergotree-ir/src/chain/ergo_box/register/id.rs	3	4	75.0%
ergotree-ir/src/type_check.rs	0	1	0.0%
ergotree-interpreter/src/eval/sbox.rs	1	3	33.33%

Files with Coverage Reduction	New Missed Lines	%
ergotree-ir/src/mir/expr.rs	2	82.23%
ergotree-interpreter/src/eval/env.rs	3	66.67%
ergotree-ir/src/serialization/types.rs	4	84.67%
ergotree-ir/src/chain/token.rs	5	72.58%

Totals
Change from base Build 6248584962:	-1.9%
Covered Lines:	10511
Relevant Lines:	12967

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💛 - Coveralls