Rf/dtype conversion performance

See merge request !20

UKB type

manually casting/coercing it all. Not implemented yet

Rf/20003

See merge request !19

convertICD10Codes function work on non-ICD10 variables

to bomb out

type to use for specific variables. Merged into the variable table as a new
"InternalType" column, which defaults to float32 if not specified in type.txt

really any need to deprecate it

hierarchicalDescriptionFrom[Code|Numeric] functions first-class metaproc
functions

numericToCode, and codeToNumeric. Lookup is performed via vid (or optionally
via data coding).

which cannot be represented with float32

specific data coding

files. Currently only coding4 description file is present.

table, and the variable ID. This is so that metaproc funcs can look up
information about the variable in question

Rf/categories

See merge request !18