doc: Spellcheck documentation ahead of 4.4 release. * aspell-octave.en.pws: Add new words to Octave-only spelling dictionary. Remove exception words which are no longer used in manual. * basics.txi, bugs.txi, func.txi, geometry.txi, install.txi, matrix.txi, package.txi, plot.txi, poly.txi, preface.txi, quad.txi, sparse.txi, strings.txi, vectorize.txi, data.cc, defaults.cc, file-io.cc, pinv.cc, quadcc.cc, qz.cc, rand.cc, schur.cc, syscalls.cc, sysdep.cc, toplev.cc, amd.cc, audioread.cc, colamd.cc, dmperm.cc, symrcm.cc, quadgk.m, quadl.m, imfinfo.m, rgb2gray.m, javachk.m, usejava.m, unpack.m, fzero.m, glpk.m, pqpnonneg.m, stemleaf.m, print.m, polyfit.m, blackman.m, bicgstab.m, cgs.m, eigs.m, pcg.m, tfqmr.m, gallery.m, rosser.m, toeplitz.m, vander.m, isstrprop.m: Add @nospell{} macro around proper names and other words which aspell should not check. Correct misspellings identified by aspell.

--- a/scripts/miscellaneous/unpack.m	Mon Mar 26 22:54:24 2018 +0200
+++ b/scripts/miscellaneous/unpack.m	Mon Mar 26 10:45:04 2018 -0700
@@ -38,11 +38,11 @@
 ## Valid filetype extensions:
 ##
 ## @table @code
-## @item  bz
-## @itemx bz2
+## @item  @nospell{bz}
+## @itemx @nospell{bz2}
 ## bzip archive
 ##
-## @item gz
+## @item @nospell{gz}
 ## gzip archive
 ##
 ## @item tar