new CLI design

doc/cli-design.txt

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+A flexible music programming language powered by math.
+
+usage:
+
+cmd [FILENAME | -c SHEET_MUSIC | --syntax | --examples | --example <n>] [-e EXPR] -n NOTE[,...] [-E [-f {"stdout" | FORMAT}]] [-v CHAR=VALUE]
+
+arguments:
+    FILENAME        file path to your .blp sheet music  [default: read from stdin]
+
+options:
+    playing music:
+        -c SHEET_MUSIC
+            sheet music to read instead of reading a file
+        -n NOTE[,...], --notes NOTE[,...]
+            available notes: a list of comma-separated alphabetical note names
+        -e EXPR, --expression EXPR
+            signal expression (instrument) to generate music samples (you can use the floating-point number t for the current time in seconds, n for the indice of the currently playing note in the list of available notes starting with 0 and N for the number of available notes)  [default: sin(2*PI*n*(442+442*((n+1)/N))*t)]
+
+    exporting music:
+        -E, --export
+            export audio instead of playing it
+        -f, --format
+            audio format to use for exporting with -E
+
+    advanced sheet music tweaking:
+        -v VARIABLE=VALUE, --variable VARIABLE=VALUE
+            add a variable named VARIABLE (an single letter) for the sheet music and all expressions and set its initial value to VALUE (you can override n, t and T)
+        -m NAME:EXPANSION, --macro MACRO:EXPANSION
+            add a macro named NAME (single character, must not be alphanumeric) which expands to EXPANSION when called in the sheet music
+        -s NAME:VARIABLE=EXPR, --slope VARIABLE=EXPR
+            add a slope expression named NAME which replaces the value of VARIABLE with the result of EXPR each frame (EXPR can use all available variables and instrument variables plus the variables α for the initial value of VARIABLE, β for the final value and Δ for the total duration of the specific slope)
+
+    help:
+        --syntax
+            show a help message about expression and sheet music syntax
+        --examples
+            show a list of expression and sheet music examples
+        --example <n>
+            show the nth example from the list provided by --examples