generalize g_to_c/n as g_to_t to simultaneously support coding and non-coding transcripts

[reece]

Originally reported by: Reece Hart (Bitbucket: reece, GitHub: reece)

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If a user fetches accessions from relevant_transcripts(), they may including coding and non-coding.

When using those transcripts, users should call g_to_c with coding transcripts and g_to_n with non-coding transcripts. Calling g_to_c with a non-coding transcript results in an exception.

This proposal is to add g_to_t, with a call signature identical to g_to_c/n, that will transparently project to the correct type.

Conversely, a general t_to_g method would project from either transcript type to genomic coordinates.

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• Bitbucket: https://bitbucket.org/biocommons/hgvs/issue/316

[reece]

Original comment by Reece Hart (Bitbucket: reece, GitHub: reece):

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closes #316: provide generalized transcript-to-genome projects to handle coding and non-coding transcripts transparently