Correct crypt.5 terminology (issue #29)

Solar Designer points out that a phrase used to describe DES-crypt,
“Hash size 64 bits (effectively 56),” is misleading.  Revert to
separate “hash size” and “effective key size” table entries as is
used in the Openwall version of this manpage, but omit the “effective
key size” table entry if it would be the same number as “hash size.”
Correct the `.hash` line for yescrypt as discussed in the review of
pull request #27.

Also swap two of the entries in the list of attacks that salt defeats,
for better prose flow; reference RFC 4648 when talking about ‘the
common “base64” encoding’ that hashes don’t use; and tighten up the
implementation of the `.hash` macro.

crypt.5

@@ -44,13 +44,13 @@ and then test it against each account's stored hash;
 the hash calculation must be repeated for each account.
 .TP
 2.
+It is not possible to tell whether two accounts use the same passphrase
+without successfully guessing one of the phrases.
+.TP
+3.
 Tables of precalculated hashes of commonly used passphrases
 must have an entry for each possible salt,
 which makes them impractically large.
-.TP
-3.
-It is not possible to tell whether two accounts use the same passphrase
-without successfully guessing one of the phrases.
 .PP
 All of the hashing methods are also deliberately engineered to be slow;
 they use many iterations of an underlying cryptographic primitive
@@ -103,10 +103,10 @@ is up to the hashing method.
 \(oq\fB$\fR\(cq characters
 usually delimit components,
 and the salt and hash are usually encoded as numerals in base 64.
-However, the details of the base-64 encoding vary among hashing
-methods and are usually
+The details of this base-64 encoding vary among hashing methods.
+The common \(lqbase64\(rq encoding specified by RFC 4648 is usually
 .I not
-compatible with the common \(lqbase64\(rq encoding.
+used.
 .SH AVAILABLE HASHING METHODS
 This is a list of
 .I all
@@ -123,10 +123,8 @@ and does not show the division into prefix, options, salt, and hash.
 .ad l
 .TP
 .B prefix
-.ie "\\$1"" \{\
-"" (empty string)
-.\}
-.el "\\$1"
+"\\$1"
+.if "\\$1"" (empty string)
 .TP
 .B Encoded passphrase format
 \\$2
@@ -136,10 +134,13 @@ and does not show the division into prefix, options, salt, and hash.
 .el \\$3 characters
 .ie "\\$4"7" (ignores 8th bit)
 .TP
-.TP
 .B Hash size
 \\$6 bits
-.if !"\\$5"\\$6" (effectively \\$5)
+.if !"\\$5"\\$6" \{
+.TP
+.B Effective key size
+\\$5 bits
+.\}
 .TP
 .B Salt size
 \\$7 bits
@@ -154,7 +155,7 @@ and does not show the division into prefix, options, salt, and hash.
 .br
 yescrypt is a scalable password hashing scheme designed by Solar
 Designer, which is based on Colin Percival's scrypt.
-.hash "$y$" "\e$y\e$[./A-Za-z0-9]+\e$[./A-Za-z0-9]*\e$[./A-Za-z0-9]{43}" unlimited 8 "" 256 "up to 512" "0 (default), 1 to 11 (logarithmic)"
+.hash "$y$" "\e$y\e$[./A-Za-z0-9]+\e$[./A-Za-z0-9]{,86}\e$[./A-Za-z0-9]{43}" unlimited 8 256 256 "up to 512" "1 to 11 (logarithmic)"
 .PP
 scrypt hashes previously used the "$7$" prefix, yescrypt is backward-compatible with them.
 .PP