puzzles: full help system

- embeds the upstream halibut documentation for plugin use

- currently every plugin has a copy of the help text, but in the
  future a centralized system using overlays might be better

Change-Id: Idb6eb9accc2fa786a4c6bc2b704e7cf5fd3f78dd

apps/plugins/puzzles/help.c

@@ -0,0 +1,48 @@
+#include "help.h"
+#include "lib/simple_viewer.h"
+
+void full_help(const char *name)
+{
+    int ch_num = -1;
+    /* search the help text for a chapter with this name */
+    for(int ch = 0; ch < help_numchapters; ++ch)
+    {
+        char *str = help_text + help_chapteroffsets[ch];
+        char *ptr = strchr(str, ':') + 1;
+        const char *namep = name;
+        if(*ptr++ != ' ')
+            continue;
+
+        while(*ptr == *namep && *ptr && *namep)
+        {
+            ptr++;
+            namep++;
+        }
+        if(*namep == '\0' && (*ptr == '\n' || *ptr == ' ')) /* full match */
+        {
+            ch_num = ch;
+            break;
+        }
+    }
+    if(ch_num < 0)
+    {
+        rb->splashf(HZ * 2, "No topic found for `%s' (REPORT ME!)", name);
+        return;
+    }
+    char *buf = smalloc(help_maxlen + 1);
+    rb->memset(buf, 0, help_maxlen + 1);
+    if(ch_num < help_numchapters - 1)
+    {
+        /* safe to look ahead */
+        memcpy(buf, help_text + help_chapteroffsets[ch_num], help_chapteroffsets[ch_num + 1] - help_chapteroffsets[ch_num]);
+    }
+    else
+        rb->strlcpy(buf, help_text + help_chapteroffsets[ch_num], help_maxlen + 1);
+
+    rb->lcd_set_foreground(LCD_WHITE);
+    unsigned old_bg = rb->lcd_get_background();
+    rb->lcd_set_background(LCD_BLACK);
+    view_text(name, buf);
+    rb->lcd_set_background(old_bg);
+    sfree(buf);
+}