Replace 4 handouts with single consolidated handout

Changelog:
- Consolidate 4 handouts into a single multi-section handout
- Remove subdirectories to avoid needing to know if someone created a directory
- Load relevant libraries in each major section
- Change h2s to h3 (because now subheadings)
- set all code comments to single #
- Rename "Subsetting Data" (starting with data) to "Subsetting Data in Dataframes" to avoid duplicate section labels
- Remove `working with data` section (data wrangling) as duplicative
- Move `%>%` explanation to when first used
- Move logical operators section to before they are used instead of immediately after
- Replace original location of `%>%` explanation with note on chaining operations
- Ensure all continuation lines (including after %>%) are indented
- Correct extra `sqrt` functions in intro section
- Move additional summary functions from dplyr section to intro section
- Clarification on `data` argument in `pivot_wider()`
- move `aes()` before first ggplot code using it
- add explanations of `x` and `y` in `aes()` section
- add cursory explanation of geom_point() when first used
- standardize `( )` to `()`
- adjustments to `theme` explanations
- add `install.packages()` explanation and example
- Add instructions/examples for installing packages
- add explanation of vectorized math
- add explanation of round()
- add explanation of `:`

To do:
- Add section linking from main header
- Add notes on what episodes sections correspond to (or link episode sections from each section here)
- Link data viz section from data viz plot() command in starting with data section
- Add code with examples of summary functions in 125
- Remove `separate_rows()` or add example
- Find a better convention than - `function` -- explanation
- should output be included? Right now, it's not
- Double check that all functions/options are introduced before being used and are only introduced once
- remove `variable` language in explanations of functions for values/vectors
- clean up explanation of `:`
- Correct `names()` and `colnames()` section to be accurate
- Check that functions match those in the lesson (and add a note somewhere in a comment as to when last checked)
- should `as.factor()` be removed as less useful than `factor()`?