;lib: update emacs code-folding config

orgstruct-mode was dropped from org 9.2, and I shouldn't have been
forcing it on anyway.

The new config allows its "replacement", outshine-mode, to do similar
code folding when you press tab on any of the lines matching
outline-regexp. But only if you patch it as mentioned at
https://github.com/alphapapa/outshine/issues/77.
Enable it by, eg: (add-hook 'haskell-mode-hook 'outshine-mode)

hledger-lib/Hledger/Read.hs

@@ -1,4 +1,4 @@
---- * -*- eval: (orgstruct-mode 1); orgstruct-heading-prefix-regexp:"--- "; -*-
+--- * -*- outline-regexp:"--- \\*"; -*-
 --- ** doc
 -- In Emacs, use TAB on lines beginning with "-- *" to collapse/expand sections.
 {-|

hledger-lib/Hledger/Read/Common.hs

@@ -1,4 +1,4 @@
---- * -*- eval: (orgstruct-mode 1); orgstruct-heading-prefix-regexp:"--- "; -*-
+--- * -*- outline-regexp:"--- \\*"; -*-
 --- ** doc
 -- In Emacs, use TAB on lines beginning with "-- *" to collapse/expand sections.
 {-|

hledger-lib/Hledger/Read/CsvReader.hs

@@ -1,4 +1,4 @@
---- * -*- eval: (orgstruct-mode 1); orgstruct-heading-prefix-regexp:"--- "; -*-
+--- * -*- outline-regexp:"--- \\*"; -*-
 --- ** doc
 -- In Emacs, use TAB on lines beginning with "-- *" to collapse/expand sections.
 {-|

hledger-lib/Hledger/Read/JournalReader.hs

@@ -1,4 +1,4 @@
---- * -*- eval: (orgstruct-mode 1); orgstruct-heading-prefix-regexp:"--- "; -*-
+--- * -*- outline-regexp:"--- *"; -*-
 --- ** doc
 -- In Emacs, use TAB on lines beginning with "-- *" to collapse/expand sections.
 {-|

hledger-lib/Hledger/Read/TimeclockReader.hs

@@ -1,4 +1,4 @@
---- * -*- eval: (orgstruct-mode 1); orgstruct-heading-prefix-regexp:"--- "; -*-
+--- * -*- outline-regexp:"--- \\*"; -*-
 --- ** doc
 -- In Emacs, use TAB on lines beginning with "-- *" to collapse/expand sections.
 {-|

hledger-lib/Hledger/Read/TimedotReader.hs

@@ -1,4 +1,4 @@
---- * -*- eval: (orgstruct-mode 1); orgstruct-heading-prefix-regexp:"--- "; -*-
+--- * -*- outline-regexp:"--- \\*"; -*-
 --- ** doc
 -- In Emacs, use TAB on lines beginning with "-- *" to collapse/expand sections.
 {-|