Add ansi escape codes

text/0000-add-ansi-escape-codes.md

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+- Feature Name: add_ansi_escape_codes
+- Start Date: 2022-02-14
+- RFC PR: (leave this empty)
+- Pony Issue: (leave this empty)
+
+# Summary
+
+This RFC proposes the addition of more escape code functions to the ANSI
+primitive of the term package.
+
+# Motivation
+
+The purpose of these additional methods is to cover more of the standard ANSI
+escape codes within the stdlib.
+
+# Detailed design
+
+## Added Escape Codes
+
+- 8-bit foreground `\x1B[38;5;nm` and background `\x1B[48;5;nm` colors
+- 24-bit foreground `\x1B[38;2;r;g;bm` and background `\x1B[48;2;r;g;bm` colors
+- enter alternate screen buffer `\x1B[?1049h` and leave alternate screen buffer `\x1B[?1049l`
+- bell alert `\x7`
+- scroll up `\x1B[nS` and scroll down `\x1B[nT`
+- next line `\x1B[nE` and previous line `\x1B[nF`
+- cursor horizontal absolute `\x1B[nG`
+- hide cursor `\x1B[?25l` and show cursor `\x1B[?25h`
+- save cursor position `\x1B[s` and restore cursor position `\x1B[u`
+- device status report `\x1B[6n` (sends cursor position to stdin)
+- faint `\x1B[2m`, italic `\x1B[3m`, conceal `\x1B[8m`, and strike `\x1B[9m` text
+- erase in display `\x1B[nJ`
+- erase in line  `\x1B[nK`
+
+
+## Erase In Display/Line
+
+There are currently two similar functions, but they have a couple of issues:
+
+- Neither of them expose the parameter that the escape codes take.  
+- The `clear` function moves the cursor to the top left and then clears the screen.  
+This may have been done to create the same result that this escape code gave on DOS.
+
+Unlike the other added escape codes, these two only have a few valid values
+for the parameters.  
+To enforce the safety of these functions using the type system, four primitives
+and two type unions would be defined to be used as the parameters for these
+two functions.
+
+```pony
+primitive EraseAfter
+primitive EraseBefore
+primitive EraseAll
+primitive EraseBuffer
+
+type EraseDisplay is (EraseAfter | EraseBefore | EraseAll | EraseBuffer)
+type EraseLine is (EraseAfter | EraseBefore | EraseAll)
+```
+# How We Teach This
+
+The added functions would be documented as the existing functions on the `ANSI`
+primitive are and an example of usage would be added to `ANSI`.
+
+# How We Test This
+
+The functions that have parameters would have tests added to ensure that they
+return the correct escape code for the given parameters.
+
+The functions that would have parameters and would be tested are:
+
+- 8-bit and 24-bit colors for the foreground and background
+- scroll up and scroll down
+- next line and previous line
+- cursor horizontal absolute
+- erase_display
+- erase_line
+
+# Drawbacks
+
+Some escape codes may not work on all terminals.
+
+# Alternatives
+
+Don't add these escape code functions and have users look up and print the
+escape codes they want.
+
+# Unresolved questions
+
+None