Throw an error if Accordion size is changed to <1

fixes #27

README.markdown

@@ -7,7 +7,7 @@ Accordion lets you set the maximum number of vsplits you want to see, and shrink
 
 If you want to view changes to a file over time, it's got a fancy diff mode. Even if you're not big on vsplits, you may want to consider Accordion for this feature alone.
 
-Version 0.3.2
+Version 0.3.3
 
 But I Don't Use Splits!
 -----------------------

autoload/accordion.vim

@@ -100,12 +100,20 @@ endfunction
 function! accordion#ChangeSize(change)
   "change tab variable if it exists
   if exists("t:accordion_size")
-    let t:accordion_size += a:change
-    call accordion#Accordion()
+    if t:accordion_size + a:change >= 1
+      let t:accordion_size += a:change
+      call accordion#Accordion()
+    else
+      echoerr "Accordion size can't be less than 1"
+    endif
   "else change global if it exists
   elseif exists("g:accordion_size")
-    let g:accordion_size += a:change
-    call accordion#Accordion()
+    if g:accordion_size + a:change >= 1
+      let g:accordion_size += a:change
+      call accordion#Accordion()
+    else
+      echoerr "Accordion size can't be less than 1"
+    endif
   "no tab or global setting to change
   else
     echom "Accordion can't change size; none set."

doc/accordion.txt

@@ -58,6 +58,7 @@ ZOOMING                                          *accordion-zooming*
 :AccordionZoomIn                                 *:AccordionZoomIn*
     Subtract 1 from maximum number of vsplits
     Tries to modify tab setting. If there is none, modifies global setting
+    Raises an error if the new size would be less than 1
 
 :AccordionZoomOut                                *:AccordionZoomOut*
     Add 1 to maximum number of vsplits