Allow for fixed string match in colname sub()

[t-morrison]

I was not able to create a plot when my grouping variable had a value with an open parenthesis in it. Digging into the code I found that the sub() function used in column name renaming was not able to parse the values with the parentheses correctly. Added this option to set fixed=TRUE in sub(), which seems to work.

[codecov-io]

Codecov Report

Merging #19 into master will increase coverage by 0.21%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #19      +/-   ##
==========================================
+ Coverage   91.18%   91.39%   +0.21%     
==========================================
  Files           9        9              
  Lines         363      372       +9     
==========================================
+ Hits          331      340       +9     
  Misses         32       32              

Impacted Files	Coverage Δ
R/c3.R	84.84% <100.00%> (+1.51%)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 94985a3...4fc6798. Read the comment docs.

[t-morrison]

I ran the test, looked OK, and fixed the comments.

[mrjoh3]

thanks @moman822 changes merged

[mrjoh3]

@moman822 do you have a small code snippet that demonstrates the new functionality? If so please send through and I will add it to the examples vignette.

thanks