QoL improvements during development

[serkor1]

📚 What?

During the development of #77 there were alot of waiting between commits locally because devtools::document() compiles the vendored TA-Lib, which then gets recompiled (again) during R CMD build.
This is (really) tedious, and not necessary.

📋 Possible improvement steps

1. Run devtools::document() conditional on changes in R/, src/ and/or man-roxygen. This could (probably) be done with git diff --exit-code (source).
2. Run CMake in configure conditional on built TA-Lib libraries and headers.

Note

Its unclear how 2. will behave on CRAN. A robust approach could possibly be that the conditional checks of TA-Lib are done conditional on NOT being on CRAN via environment variables.

If 2 is implemented, then 1. is redundant to some degree, because devtools::document() is fast enough by itself.

🔨 Plan of attack

The Makefile is already messy as-is. To avoid further mess, a collection of BASH scripts could be used ti achieve it.