Handle error in capture_str

[renkun-ken]

What problem did you solve?

Closes #755

capture_str now handles error internally in the following way:

1. Capture str() with user specified max.level.
2. If error occurs, fall back to show class.

(If you do not have screenshot) How can I check this pull request?

The following examples no longer produce errors:

Simple flawed str:

errobj <- structure(list(x = 1), class = "err")
str.err <- function(obj) 0 + obj
options(vsc.str.max.level = 1)

Original issue with flawed str implementation:

library(tidyverse)
library(igraph)
library(tidygraph)

# setting workspace level to anything > 0 creates error
options(vsc.str.max.level = 1)

# create a simple igraph object
g <- erdos.renyi.game(10, .1)

# converting to a tbl_graph object produces the error (note that code still runs)
g <- as_tbl_graph(g)

[ElianHugh]

Works as expected, thank you for the quick fix!