Replace fixed size blocks with linked list

[ChAoSUnItY]

This PR adjusts size of blocks array based on demand instead of using a constant, to prevent potential insufficient allocation issues in the future work, also reduces memory usage when compiling small programs.

I use /usr/bin/time -v ./out/shecc tests/hello.c to benchmark the usage of memory:

Before:

Command being timed: "./out/shecc tests/hello.c"
        User time (seconds): 0.00
        System time (seconds): 0.06
        Percent of CPU this job got: 93%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.07
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 224528
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 11436
        Voluntary context switches: 2
        Involuntary context switches: 0
        Swaps: 0
        File system inputs: 16
        File system outputs: 32
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0

After:

Command being timed: "./out/shecc tests/hello.c"
        User time (seconds): 0.00
        System time (seconds): 0.02
        Percent of CPU this job got: 100%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.02
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 51852
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 12204
        Voluntary context switches: 1
        Involuntary context switches: 1
        Swaps: 0
        File system inputs: 0
        File system outputs: 32
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0

[jserv]

Improve git commit messages.

[jserv]

Refine the git commit messages:

• Wrap the body at 72 characters
• Use the body to explain what and why vs. how

[jserv]

Thank @ChAoSUnItY for contributing!