fix: linter issues in specs/DataStructures/Account (#493)

- remove unused link declarations
- surround titles and code with blank lines
- give fenced code a language (using c to format comments)

specs/DataStructures/Account.md

@@ -2,8 +2,6 @@
 
 ## Account ID
 
-[account_id]: #account_id
-
 NEAR Protocol has an account names system. Account ID is similar to a username. Account IDs have to follow the rules.
 
 ### Account ID Rules
@@ -26,6 +24,7 @@ Regex for a full account ID, without checking for length:
 ```regex
 ^(([a-z\d]+[\-_])*[a-z\d]+\.)*([a-z\d]+[\-_])*[a-z\d]+$
 ```
+
 ### Top Level Accounts
 
 | Name | Value |
@@ -52,7 +51,7 @@ def action_create_account(predecessor_id, account_id):
 
 Valid accounts:
 
-```
+```c
 ok
 bowen
 ek-2
@@ -73,7 +72,7 @@ bro.a
 
 Invalid accounts:
 
-```
+```c
 not ok           // Whitespace characters are not allowed
 a                // Too short
 100-             // Suffix separator
@@ -91,6 +90,7 @@ abcdefghijklmnopqrstuvwxyz.abcdefghijklmnopqrstuvwxyz.abcdefghijklmnopqrstuvwxyz
 ```
 
 ## System account
+
 `system` is a special account that is only used to identify refund receipts. For refund receipts, we set the predecessor_id to be `system` to indicate that it is a refund receipt. Users cannot create or access the `system` account. In fact, this account does not exist as part of the state. 
 
 ## Implicit account IDs
@@ -107,6 +107,7 @@ The corresponding secret key allows you to sign transactions on behalf of this a
 ### Implicit account creation
 
 An account with implicit account ID can only be created by sending a transaction/receipt with a single `Transfer` action to the implicit account ID receiver:
+
 - The account will be created with the account ID.
 - The account will have a new full access key with the ED25519-curve public key of `decode_hex(account_id)` and nonce `0`.
 - The account balance will have a transfer balance deposited to it.
@@ -117,8 +118,6 @@ Once an implicit account is created it acts as a regular account until it's dele
 
 ## Account
 
-[account]: #account
-
 Data for an single account is collocated in one shard. The account data consists of the following:
 
 - Balance