add support for log scale axis in chart_Series

[ethanbsmith]

Description

Neither of these approaches produce a log scaled y axis

chart_Series(x, log.scale=TRUE)  # like in chartSeries()
chart_Series(x, log="y")         # like in plot.default()

This problem was also identified at : https://stackoverflow.com/questions/25261388/does-chart-series-work-with-logarithmic-axis

Expected behavior

some parameter that will allow at least the y axis to be log scaled. ideally this would also work TA panels

Session Info

> sessionInfo()
R version 3.6.3 (2020-02-29)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 18363)

Matrix products: default

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252    LC_MONETARY=English_United States.1252 LC_NUMERIC=C                           LC_TIME=English_United States.1252    

attached base packages:
[1] parallel  stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] rio_0.5.16        rvest_0.3.4       xml2_1.2.2        data.table_1.12.2 curl_4.2          quantmod_0.4-15   TTR_0.23-5        xts_0.11-2        zoo_1.8-6         RODBC_1.3-16      doParallel_1.0.15 iterators_1.0.12 
[13] foreach_1.4.7     plotrix_3.7-6     checkpoint_0.4.7 

loaded via a namespace (and not attached):
 [1] Rcpp_1.0.2       magrittr_1.5     hms_0.5.1        lattice_0.20-38  R6_2.4.0         rlang_0.4.0      httr_1.4.1       tools_3.6.3      grid_3.6.3       readxl_1.3.1     tibble_2.1.3     crayon_1.3.4     zip_2.0.4       
[14] vctrs_0.2.0      codetools_0.2-16 zeallot_0.1.0    haven_2.1.1      openxlsx_4.1.0.1 cellranger_1.1.0 pillar_1.4.2     compiler_3.6.3   backports_1.1.4  forcats_0.4.0    foreign_0.8-75   pkgconfig_2.0.3 
> 

[ethanbsmith]

while this could be handled through a pars parameter, the same could have been done for the original chartSeries. i think adding a log.scale parameter to the chart_Series function signature, that gets passed through to plot.xts is the better design.

[ethanbsmith]

dependent on joshuaulrich/xts#103