Support a environment variable,

[HughParsonage]

This changes the default value of path throughout to consistently support an environment variable R_READABS_PATH.

The advantages of this method are:

1. Compliance with WRE. (I suspect by using data/ABS as the default, you're technically noncompliant e.g. in the vignette, so it would be good to fix this before CRAN notices).
2. Allows multiple sessions/projects on the same computer (even across reboots) to use the same path, rather than each using data/ABS by default or requiring each instance of read_abs to specify the same path (which reduces portability).
3. As you note in the vignette, you have to specify path when selecting subtables. Referring to an environment variable, or encouraging its use, might make that step redundant. There are other enhancements I had in mind if you think this is a positive addition, including some related to add ability to check if local file exists & is up to date #46 .

Note that this is a backwards incompatible change if a user had not specified path in read_abs but did in read_abs_local. (However, if they specified neither, or both, their code should still work.)

I thought about a package option but this can't be easily set between sessions so would not be as useful.

[codecov]

Codecov Report

Merging #47 into master will decrease coverage by 2.3%.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master   #47      +/-   ##
=======================================
- Coverage    92.3%   90%   -2.31%     
=======================================
  Files          14    15       +1     
  Lines         351   360       +9     
=======================================
  Hits          324   324              
- Misses         27    36       +9

Impacted Files	Coverage Δ
R/read_abs_local.R	81.25% <ø> (ø)	⬆️
R/read_abs.R	88.13% <ø> (ø)	⬆️
R/read_cpi.R	100% <ø> (ø)	⬆️
R/download_abs.R	100% <ø> (ø)	⬆️
R/extract_abs_sheets.R	93.75% <ø> (ø)	⬆️
R/zzz.R	0% <0%> (ø)

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[MattCowgill]

Thanks @HughParsonage, I'll review this as soon as I can (Monday at latest)

[MattCowgill]

This is great, thanks @HughParsonage. What are the other things you had in mind?